The requirements for the design and testing of flight hardware pressure system components are described below. Included are hydraulic, pneumatic, hypergolic, and cryogenic fluid and propellant system components.
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12.5.1. Flight Hardware Pneumatic and Hydraulic Pressure System Components
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12.5.1.1. Factor of Safety Requirements. Flight hardware pneumatic and hydraulic pressure system components shall be designed to the minimum factors shown in Table 12.3.
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Table 12.3. Pressure Components Safety Factors.
Component
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Proof
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Design Burst
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Lines and fittings diameter < 1.5 inches (38 mm)
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1.5
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4.0
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Lines and fittings diameter > 1.5 inches (38 mm)
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1.5
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2.5
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Fluid Return Sections
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1.5
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3.0
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Fluid Return Hose
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1.5
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5.0
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Other Pressure Components
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1.5
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2.5
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Components subject to low or negative pressure shall be evaluated at 2.5 times maximum external pressure expected during service life.
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12.5.1.2. Flight Hardware Pneumatic and Hydraulic Pressure System Component General Selection and Design Requirements
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12.5.1.2.1. Components shall be selected to ensure that misconnections or reverse installations within the subsystem are not possible. Color codes, labels, and directional arrows shall be used to identify hazards and direction of flow.
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12.5.1.2.2. The maximum fluid temperature shall be estimated early in design as part of data for selection of safety critical components, such as system fluid, pressurizing gas, oil coolers, and gaskets.
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12.5.1.2.3. Components that are capable of safe actuation under pressure equal to the maximum relief valve setting in the circuit in which they are installed shall be specified.
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12.5.1.2.4. Pumps, valves and regulators, hoses, and all such prefabricated components of a pressure system shall have proven pressure service ratings equal to or higher than the limit load (MEOP) and rated life of the system.
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12.5.1.2.5. The Standards of the Hydraulic Institute shall be used in evaluating safety in pump selection.
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12.5.1.2.6. Where leakage or fracture is hazardous to personnel or critical equipment, valves shall be selected so that failure occurs at the outlet threads of valves before the inlet threads or body of the valve fails under pressure.
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12.5.1.2.7. Pressure regulators shall be selected to operate in the center 50 percent of their total pressure range and avoid creep and inaccuracies at either end of the full operating range.
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12.5.1.2.8. In all cases, flareless tube fittings shall be properly preset before pressure application.
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12.5.1.2.9. Where system leakage can expose hydraulic fluid to potential ignition sources or is adjacent to a potential fire zone and the possibility of flame propagation exists, fire-resistant or flame-proof hydraulic fluid shall be used.
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12.5.1.3. Flight Hardware Oxygen System Components
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12.5.1.3.1. For oxygen systems of 3,000 psi or higher, valves and other components that are slow opening and closing types shall be selected to minimize the potential for ignition of contaminants.
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12.5.1.3.2. Oxygen systems shall require electrical grounding to eliminate the possibility of the buildup of static electrical charges.
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12.5.1.3.3. Oxygen system components, design, and material selection shall conform to ASTM MNL 36.
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12.5.1.4. Flight Hardware Pneumatic and Hydraulic System Manual Valves and Regulators
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12.5.1.4.1. Manually operated valves and regulators shall be selected so that overtorquing of the valve stem of the regulator adjustment cannot damage soft seats to the extent that failure of the seat will result.
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12.5.1.4.2. Valve designs that use uncontained seals are unacceptable and shall not be selected.
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12.5.1.5. Flight Hardware Pneumatic and Hydraulic System Warning Devices and Safety Critical Components
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12.5.1.5.1. Warning devices that are activated by hazardous over or under pressure shall be selected whenever necessary.
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12.5.1.5.2. The warning device shall either activate automatic response mechanisms or shall notify operational personnel of impending hazards.
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12.5.1.5.3. Warning devices to indicate hazardous over or under pressures to operating personnel shall be specified.
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12.5.1.5.4. These warning devices shall actuate at predetermined pressure levels designed to allow time for corrective action.
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12.5.1.5.5. Safety critical actuation of pneumatic systems shall not be adversely affected by any back pressure resulting from concurrent operations of any other parts of the system under any set of conditions.
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12.5.1.5.6. Components that can be isolated and contain residual pressure shall be equipped with gage reading and bleed valves for pressure safety checks.
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12.5.1.5.7. Bleed valves shall be directed away from operating personnel.
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12.5.1.5.8. Fittings or caps for bleeding pressure are not acceptable.
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12.5.1.5.9. Pressurized reservoirs that are designed for gas/fluid separation with provisions to entrap gas that may be hazardous to the system or safety critical actuation and prevent its recirculation in the system shall be specified. Specific instructions shall be posted adjacent to the filling point for proper bleeding when servicing.
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12.5.1.5.10. Compressed gas emergency systems shall be bled directly to the atmosphere away from the vicinity of personnel rather than to reservoir.
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12.5.1.5.11. If the gas is combustible, safety critical components shall be utilized and methods for reducing the potential for accidental ignition or explosion shall be assessed, controlled as required, and verified and documented through a hazard analysis.
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12.5.1.5.12. Where necessary to prevent a hazardous sequence of operations and provide a fail-safe capability at all times, interlocks shall be specified. For example, the OPEN position of remotely controlled valves that can hazardously pressurize lines leading to remotely controlled (or automatic) disconnect couplings shall be interlocked to preclude the OPEN valve position coincident with the disconnected condition of the couplings.
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12.5.1.5.13. Pressure systems that combine several safety critical functions shall have sufficient controls for isolating failed functions for the purpose of safely operating the remaining functions.
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12.5.1.5.14. All pressure systems shall have pressure indicating devices to monitor critical flows and pressures marked to show safe upper and lower limits of system pressure.
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12.5.1.5.15. The pressure indicators shall be located to be readily visible to the operating crew.
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12.5.1.5.16. All systems shall be protected for pressure above 500 psi in all areas where damage can occur during servicing or other operational hazards.
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12.5.1.5.17. Pressure lines and components of 500 psi or higher that are adjacent to safety critical equipment shall be shielded to protect such equipment in the event of leakage or burst of the pressure system.
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12.5.1.5.18. Automatic disengagement or bypass shall be provided for pneumatic systems that provide for manual takeover in the event of a hazardous situation.
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12.5.1.5.19. Positive indication of disengagement shall be provided.
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12.5.1.5.20. Safety critical pneumatic actuators shall have positive mechanical stops at the extremes of safe motion.
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12.5.1.5.21. Adjustable orifice restrictor valves shall not be used in safety critical pneumatic systems.
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12.5.1.6. Flight Hardware System Pneumatic Components
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12.5.1.6.1. Pneumatic components (other than tanks) for safety critical systems shall exhibit safe endurance against hazardous failure modes for not less than 400 percent of the total number of expected cycles including system tests.
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12.5.1.6.2. The configuration of pneumatic components shall permit bleeding of entrapped moisture, lubricants, particulate material, or other foreign matter hazardous to the system.
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12.5.1.6.3. Compressors that are designed to sustain not less than 2.5 times delivery pressure after allowance for loss of strength of the materials equivalent to not less than that caused by 1,000 hours aging at 275o F shall be selected.
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12.5.1.7. Flight Hardware Pneumatic and Hydraulic System Design Loads
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12.5.1.7.1. Installation of all lines and components to withstand all expected acceleration and shock loads shall be specified.
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Shock isolation mounts may be used if necessary to eliminate destructive vibration and interference collisions.
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12.5.1.7.2. The mounting of components, including valves, on structures having sufficient strength to withstand torque and dynamic loads and not supported by the tubing shall be specified.
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12.5.1.7.3. Light-weight components that do not require adjustment after installation (for example, check valves) may be supported by the tubing, provided that a tube clamp is installed on each such tube near the component.
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12.5.1.7.4. Tubing shall be supported by cushioned steel tube clamps or by multiple-block type clamps that are suitably spaced to restrain destructive vibration.
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12.5.1.8. Flight Hardware Pneumatic and Hydraulic System Electrical and Electronic Devices
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12.5.1.8.1. Electrical components for use in potentially ignitable atmospheres shall be demonstrated to be incapable of causing an explosion in the intended application.
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12.5.1.8.2. Electrically energized hydraulic components shall not propagate radio-frequency energy that is hazardous to other subsystems in the total system, or interfere in the operation of safety critical electronic equipment. (See MIL-STD-464, Systems Electromagnetic Environmental Effects Requirements.)
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12.5.1.8.3. Pressure system components and lines shall be electrically grounded to metallic structures.
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12.5.1.8.4. All solenoids shall be capable of safely withstanding a test voltage of not less than 1500 V rms at 60 cps for 1 minute between terminals and case at the maximum operating temperature of the solenoid in the functional envelope.
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12.5.1.8.5. Electric motor-driven pumps used in safety critical systems shall not be used for ground test purposes unless the motor is rated for reliable, continuous, and safe operation. Otherwise, the test parameters may perturb reliability calculations.
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12.5.1.9. Flight Hardware Pneumatic and Hydraulic System Pressure Relief Devices
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12.5.1.9.1. Pressure relief devices shall be specified on all systems having a pressure source that can exceed the maximum allowable pressure of the system or where the malfunction/failure of any component can cause the maximum allowable pressure to be exceeded.
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12.5.1.9.2. Relief devices are required downstream of all regulating valves and orifice restrictors unless the downstream system is designed to accept full source pressure.
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12.5.1.9.3. On payload systems, where operational or weight limitations preclude the use of relief valves and systems operate in an environment not hazardous to personnel, they can be omitted if the ground or support system contains such devices and they cannot be isolated from the spaceflight hardware pressure system during the pressurization cycle.
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12.5.1.9.4. Where safety factors of less than 2.0 are used in the design of flight hardware pressure vessels, a means for automatic relief, depressurization, and pressure verification of safety critical vessels in the event of launch abort shall be provided. Spacecraft (payload) pressure vessels may be designed without automatic relief (other means of safe relief shall be provided) if a safety analysis validates that a rupture will not damage the safety systems.
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12.5.1.9.5. Whenever any pressure volume can be confined and/or isolated by system valving, an automatic pressure relief device shall be provided.
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12.5.1.9.6. Pressure relief devices shall vent toxic or inert gases to safe areas, away from the vicinity of personnel. Scrubbers or vapor disposal systems shall also be used at a safe distance from personnel.
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Pop-valves, rupture disks, blow-out plugs, armoring, and construction to contain the greatest possible overpressure that may develop are examples of corrective measures for system safety.
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12.5.1.9.7. Shut-off valves for maintenance purposes on the inlet side of pressurized relief valves are permissible if a means for monitoring and bleeding trapped pressure is provided and the requirements of ASME Boiler and Pressure Vessel (BPVC) Code for unfired pressure vessels, Section VIII Appendix M, Paragraph UA-354 are met. It is mandatory that the valve be locked open when the system is repressurized.
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12.5.1.9.8. Hydrostatic testing systems for vessels that are not designed to sustain negative internal pressure shall be equipped with fail-safe devices for relief of hazardous negative pressure during the period of fluid removal.
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Check valves and valve interlocks are examples of devices that can be used for this purpose.
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12.5.1.9.9. Vessels that can be collapsed by a negative pressure shall have negative pressure relief and/or prevention devices for safety during storage and transportation.
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12.5.1.9.10. Pressurized reservoirs shall be designed so that all ullage volumes are connected to a relief valve that shall protect the reservoir and power pump from hazardous overpressure or back pressure of the system.
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12.5.1.9.11. The air pressure control for pressurized reservoirs shall be an externally nonadjustable, pressure regulating device. If this unit also contains a reservoir pressure relief valve, it shall be designed so that no failure in the unit permits overpressurization of the reservoir.
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12.5.1.10. Flight Hardware Pneumatic and Hydraulic System Contamination. Contamination shall be prevented from entering or developing in safety and safety critical flight hardware pneumatic or hydraulic system components. Safety and safety critical systems shall be designed to include provisions for detection, filtration, and removal of contaminants.
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1. The following contamination-related considerations should be addressed in the design of pressurized systems. Contamination includes solid, liquid, and gaseous material.
a. Contamination should be prevented from entering or developing within the system.
b. The system should be designed to include provisions to detect contamination.
c. The system should be designed to include provisions for removal of contamination and provisions for initial purge with fluid or gas that cannot degrade future system performance. The system should be designed to be tolerant of contamination.
2. All pressurizing fluids entering safety critical system should be filtered through a 10 micron filter, or finer, before entering the system.
3. All pressure systems should have fluid filters in the system, designed and located to reduce the flow of contaminant particles to a safe minimum.
4. All of the circulating fluid in the system should be filtered downstream from the pressure pump or immediately upstream from safety critical actuators.
5. Entrance of contamination at test points or vents should be minimized by downstream filters.
6. The bypass fluid or case drain flow on variable displacement pumps should be filtered.
7. When the clogging of small orifices could cause a hazardous malfunction or failure of the system, they should be protected by a filter element designed to prevent clogging of the orifice. Note that this includes servo valves.
8. Filters or screens should not be used in suction lines of power pumps or hand pumps of safety critical systems.
9. Air filters should be specified for hydraulic reservoir air pressurization circuits and located to protect the pressure regulating equipment from contamination.
10. Dry compressed air should be specified for hydraulic reservoir pressurization.
11. A moisture removal unit should be specified to protect the pressure regulation lines and equipment.
12. Unpressurized Reservoirs. Unpressurized hydraulic reservoirs should have filters and desiccant units at the breather opening to preclude introduction of moisture and contaminants into the reservoir.
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12.5.1.11. Flight Hardware Pneumatic and Hydraulic System Bleed Ports
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12.5.1.11.1. Where necessary, bleed ports shall be provided to remove accumulations of residue or contaminants.
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12.5.1.11.2. High point bleed ports shall be provided where necessary for removal of trapped gases.
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12.5.1.11.3. The bleed valve shall be directed away from operating personnel and possible ignition sources.
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12.5.1.11.4. Components, cavities, or lines that can be isolated shall be equipped with bleed valves that can be used to release retained pressure, or they shall indicate that continued pressure exists in the system.
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12.5.1.11.5. Bleed valves used for reducing pressure on systems containing hazardous fluids shall be routed to a safe disposal area.
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12.5.1.11.6. Auxiliary Bleed Ports
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12.5.1.11.6.1. Auxiliary bleed ports shall be provided where necessary to allow bleed off for safety purposes.
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12.5.1.11.6.2. Bleeder valves shall be located so that they can be operated without removal of other components, and shall permit the attachment of a hose to direct the bleed-off fluid into a container.
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12.5.1.11.7. Reservoir filler caps shall include design provisions that shall automatically bleed the reservoir on opening so that possible ullage pressure cannot impart hazardous kinetic energy to either the filler caps, the fluid in the reservoir, or the system.
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12.5.1.12. Flight Hardware Pneumatic and Hydraulic System Control Devices
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12.5.1.12.1. Safety critical pressure systems incorporating two or more directional control valves shall be designed to preclude the possibility of inadvertently directing the flow or pressure from one valve into the flow path or pressure path intended for another valve, with any combination of valve settings possible in the total system.
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12.5.1.12.2. Control devices shall be designed to prevent overtravel or undertravel that may contribute to a hazardous condition or damage to the valve.
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12.5.1.12.3. All pressure and volume controls shall have stops, or equivalent, to prevent settings outside their nominal safe working ranges.
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12.5.1.12.4. Control components that have integral manually operated levers and stops shall be capable of withstanding the following limit torques in Table 12.4.
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Table 12.4. Limit Torque Requirements.
Lever Radius
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Design Torque
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Less than 3 inches
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50 x R inch-pound
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3 to 6 inches
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75 x R inch-pound
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Over 6 inches
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150 x R inch-pound
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12.5.1.13. Flight Hardware Pneumatic and Hydraulic System Manually Operated Levers
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12.5.1.13.1. Components that have integrated manually operated levers shall provide levers and stops capable of withstanding the limit torques specified by MIL-STD-1472.
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12.5.1.13.2. Levers and stops shall be provided on remote controls capable of withstanding a limit torque of 1,800 inch-pounds.
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12.5.1.13.3. Because jamming is possible, sheathed flexible actuators shall not be used for valve controls in safety critical pressure systems (for example, push-pull wires and torque wires that are sheathed are not acceptable).
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12.5.1.14. Flight Hardware Pneumatic and Hydraulic System Accumulators
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12.5.1.14.1. Accumulators shall be designed in accordance with the pressure vessel standards for ground systems and located for minimal probability of mechanical damage and for minimum escalation of material damage or personnel injury in the event of a major failure such as tank rupture.
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12.5.1.14.2. Accumulator gas pressure gauges shall not be used to indicate system pressure for operational or maintenance purposes.
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12.5.1.14.3. Gas type and pressure level shall be posted on, or immediately adjacent to, the accumulator.
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12.5.1.15. Flight Hardware Pneumatic and Hydraulic System Flexible Hose. Flexible hose requirements are specified in 12.1.10.4.
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12.5.1.16. Flight Hardware Pneumatic and Hydraulic System Qualification Test Requirements. Qualification tests are not required on lines and fittings. Internal/external pressure testing shall be conducted on all other pressure components to demonstrate no failure at the design burst pressure. Seamless lines, tubing, and pipe are exempt.
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12.5.1.17. Flight Hardware Pneumatic and Hydraulic System Acceptance Test Requirements
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12.5.1.17.1. Testing Flight Hardware Pneumatic and Hydraulic Components Before Assembly
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12.5.1.17.1.1. All pressurized components such as valves, pipe, tubing, and pipe and tube fittings shall be hydrostatically proof tested to a minimum of 1.5 times the component MAWP for a minimum of 5 minutes.
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12.5.1.17.1.2. Proof testing shall demonstrate that the components sustain proof pressure levels without distortion, damage, or leakage.
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12.5.1.17.1.3. Both the inlet and discharge sides of a relief valve shall be proof tested. When the discharge side has a lower pressure rating than the inlet, they are to be proof tested independently.
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12.5.1.17.1.4. The following inspections shall be performed after proof testing:
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12.5.1.17.1.4.1. Mechanical components such as valves and regulators shall be inspected for external deformation, deterioration, or damage.
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12.5.1.17.1.4.2. Damaged, distorted, or deteriorated parts shall be rejected and replaced and the test repeated.
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12.5.1.17.1.5. Functional and leak tests shall be performed at the component MAWP after the proof test.
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12.5.1.17.1.6. Pneumatic pressure system components shall undergo sufficient qualification and acceptance testing to demonstrate that the system and components meet design and safety requirements when subjected to prelaunch and launch environments such as vibration, shock, acceleration, and temperature.
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12.5.1.17.1.7. Test plans and test reports shall be submitted to the PSWG and made available to the PSWG and Range Safety.
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12.5.1.17.1.8. Pressure relief valves shall be tested for proper setting and flow capacity before installation and first use on the ranges.
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12.5.1.17.1.9. Pressure transducers shall be hydrostatically tested to a minimum of 1.5 times the system MOP/MEOP.
Note: Depending upon the manufacturer or model of the pressure transducer, it may not be possible to hydrostatically test it to a minimum 1.5 times MOP/MEOP without causing a shift in the transducer. This is dependent on the transducer’s specification and manufacturer’s recommendations for the transducer.
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12.5.1.17.1.10. Pressure transducers shall be calibrated before installation and periodically thereafter as recommended by the manufacturer.
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12.5.1.17.1.11. Components may be initially hydrostatically proof tested after being assembled into a subsystem to 1.5 times the system MOP. This approach requires prior approval from the PSWG and Range Safety.
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12.5.1.17.1.12. Pneumatic proof testing to a proof pressure of 1.25 times MAWP is permissible only if hydrostatic proof testing is impractical, impossible, or jeopardizes the integrity of the system or system element. Prior approval for pneumatic proof testing at the payload processing facility and/or launch site area shall be obtained from the local safety authority.
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12.5.1.17.2. Testing Flight Hardware Pneumatic and Hydraulic Systems After Assembly. All newly assembled pressure systems shall be hydrostatically tested to 1.5 times MOP/MEOP before use. MOP here refers to the maximum operating pressure that personnel are exposed to. Where this is not possible, the PSWG and Range Safety shall determine the adequacy of component testing and alternate means of testing the assembled system.
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12.5.1.17.3. Flight Hardware Pneumatic and Hydraulic System Leak Tests
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12.5.1.17.3.1. All newly assembled pressure systems shall undergo a dedicated leak test at the system MOP/MEOP before first use at any payload processing facility and launch site area.
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12.5.1.17.3.2. This test shall be conducted at the payload processing facility and launch site area unless prior approval from the PSWG and Range Safety has been obtained.
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12.5.1.17.3.3. Minimum test requirements are as follows:
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12.5.1.17.3.3.1. The media used during the leak test shall be the same as the system fluid media. For hazardous gas systems, a system-compatible, non-hazardous gas may be used that has a density as near as possible to the operating system gas; for example, helium should be used to leak test a gaseous hydrogen system.
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12.5.1.17.3.3.2. Mechanical connections, gasketed joints, seals, weld seams, and other items shall be visually bubble tight for a minimum of 1 minute when an approved leak test solution is applied.
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12.5.1.17.3.3.3. Alternate methods of leak testing (such as the use of portable mass spectrometers) may be specified when required on a case-by-case basis.
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12.5.1.17.4. Flight Hardware Pneumatic and Hydraulic System Validation and Functional Tests
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12.5.1.17.4.1. All newly assembled pressure systems shall have a system validation test and a functional test of each component at system MOP before first use at the payload processing facility and/or launch site area.
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12.5.1.17.4.2. These tests shall be conducted at the payload processing facility and launch site area unless prior approval from the PSWG and Range Safety has been obtained.
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12.5.1.17.4.3. Minimum test requirements are as follows:
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12.5.1.17.4.3.1. These tests shall demonstrate the functional capability of all non-passive components such as valves, regulators, and transducers.
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12.5.1.17.4.3.2. All prelaunch operational sequences for the system shall be executed.
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12.5.1.17.4.3.3. All parallel or series redundant components shall be individually tested to ensure all failure tolerant capabilities are functional before launch.
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12.5.1.17.4.3.4. All shutoff and block valves shall be leak checked downstream to verify their shutoff capability in the CLOSED position.
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12.5.1.17.5. Flight Hardware Pneumatic and Hydraulic System Bonding and Grounding Tests. All newly assembled pressure systems containing flammable and combustible fluids or media shall be tested to verify that the requirements of 12.1.12 of this volume have been met.
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12.5.1.17.6. Test Requirements for Modified and Repaired Flight Hardware Pneumatic Systems
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12.5.1.17.6.1. Any pressure system element, including fittings or welds, that has been repaired, modified, or possibly damaged before having been proof tested, shall be retested at proof pressure before its normal use.
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12.5.1.17.6.2. A modified or repaired pressure system shall be leak tested at the system MOP/MEOP before its normal use. This test shall be conducted at the ranges unless prior approval from the local safety authority has been obtained.
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12.5.1.17.6.3. A modified or repaired pressure system shall be revalidated and functionally tested at its operational pressures envelope up to the system MOP before its normal use.
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12.5.1.17.6.4. If any pressure system element such as a valve, regulator, gauges, or tubing has been disconnected or reconnected for any reason, the affected system or subsystem shall be leak tested at MOP/MEOP.
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12.5.2. Flight Hardware Hazardous Fluid System Components, Including Hypergolic, Cryogenic, and Hydraulic Systems. Hypergolic and cryogenic components are required to meet the requirements in 12.6, 12.7, 12.8, and 12.9 in addition to the following:
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12.5.2.1. Cycling capability for safety critical components shall be not less than 400 percent of the total number of expected cycles, including system tests, but not less than 2,000 cycles.
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12.5.2.2. For service above a temperature of 160ºF an additional cycling capability equivalent to the above shall be required as a maximum.
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12.5.2.3. Safety critical actuators shall have positive mechanical stops at the extremes of safe motion.
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12.5.2.4. Hydraulic fluid reservoirs and supply tanks shall be equipped with remotely operated shutoff valves.
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12.5.2.5. Shuttle valves shall not be used in safety critical hydraulic systems where the event of a force balance on both inlet ports may occur, causing the shuttle valve to restrict flow from the outlet port.
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12.5.2.6. Systems incorporating accumulators shall be interlocked to either vent or isolate accumulator fluid pressure when power is shutoff.
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12.5.2.7. Adjustable orifice restrictor valves shall not be used in safety critical systems.
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12.5.2.8. When two or more actuators are mechanically tied together, only one lock valve shall be used to lock all the actuators.
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12.5.2.9. Lock valves shall not be used for safety critical lockup periods likely to involve extreme temperature changes, unless fluid expansion and contraction effects are safely accounted for.
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12.5.2.10. Flight Hardware Hazardous Fluid System Reservoirs:
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12.5.2.10.1. Whenever possible, the hydraulic reservoir should be located at the highest point in the system.
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12.5.2.10.2. If the requirement in 12.5.2.10.1 is not possible in safety critical systems, procedures shall be developed to detect air in actuators or other safety critical components and to ensure that the system is properly bled before each use.
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12.5.2.11. Systems installations shall be limited to a maximum pressure of 15,000 psig.
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There is no intent to restrain development of systems capable of higher pressures; however, the use of such systems shall be preceded by complete development and qualification that includes appropriate safety tests.
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12.5.2.12. The inlet pressure of pumps in safety critical systems shall be specified to prevent cavitation effects in the pump passages or outlets.
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12.5.2.13. Safety critical systems shall have positive protection against breaking the fluid column in the suction line during standby.
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12.5.2.15. Systems that provide for manual takeover shall automatically disengage or allow by-pass of the act of manual takeover.
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12.5.2.16. Safety critical systems or alternate bypass systems provided for safety shall not be rendered inoperative because of back pressure under any set of conditions.
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12.5.2.17. The system shall be designed so that a lock resulting from an unplanned disconnection of a self-seating coupling or other component shall not cause damage to the system or to adjacent property or injury to personnel.
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12.5.2.18. Systems using power-operated pumps shall include a pressure regulating device and an independent safety relief valve.
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12.5.2.19. Flight Hardware Hazardous Fluid System Thermal Pressure Relief Valves:
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12.5.2.19.1. Thermal expansion relief valves shall be installed as necessary to prevent system damage from thermal expansion of hydraulic fluid as in the event of gross overheating.
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12.5.2.19.2. Internal valve leakage shall not be considered an acceptable method of providing thermal relief.
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12.5.2.19.3. Thermal relief valve settings shall not exceed 150 psi above the value for system relief valve setting.
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12.5.2.19.4. Vents shall outlet only to areas of relative safety from a fire hazard.
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12.5.2.19.5. Hydraulic blow-out fuses (soft plugs) shall not be used in systems having temperatures above 160oF.
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12.5.2.20. Pressure relief valves shall be located in the systems wherever necessary to ensure that the pressure in any part of a power system shall not exceed the safe limit above the regulated pressure of the system.
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