Recommended Installation Practices; Mounting Position; Inlet Piping - Baker Hughes Consolidated 4900 Series Instruction Manual

XI.

Recommended Installation Practices

A. Mounting Position
The POSRVs should be mounted in a vertical upright position (in
accordance with API RP 520). Installing a pilot operated safety relief valve in
any position other than vertical (±1 degree) will adversely affect its operation
as a result of induced misalignment of moving parts. A stop valve may be
placed between the pressure vessel and its relief valve only as permitted
by code regulations. If a stop valve is located between the pressure vessel
and POSRV, the stop valve port area should equal or exceed the nominal
internal area associated with the pipe size of the POSRV inlet. The pressure
drop from the vessel to the POSRV shall not exceed 3% of the valve's set
pressure, when flowing at full capacity.
Ensure the flanges and sealing faces of the valve and connective piping are
free from dirt, sediment, and scale. Ensure all flange bolts are drawn evenly
to prevent distortion of the valve body and the inlet nozzle. Position the
POSRVs for easy access and/or removal so that servicing can be properly
performed. Ensure sufficient working space is provided around and above
the valve.
B. Inlet Piping
The inlet piping (Figure 9) to the valve should be short and direct from the
vessel, or equipment, being protected. The radius of the connection to the
vessel should permit smooth flow to the valve. Avoid sharp corners. If this is
not practical, then the inlet should be at least one additional pipe diameter
larger. The pressure drop from the vessel to the valve shall not exceed 3%
of valve set pressure when the valve is allowing full capacity flow. The inlet
piping should never be smaller in diameter than the inlet connection of the
valve. Excessive pressure drop in gas, vapor, or flashing liquid service at
the inlet of the POSRV will cause extremely rapid opening and closing of
the valve, which is known as "chattering". Chattering will result in lowered
capacity and damage to the seating surfaces. The most desirable installation
is that in which the nominal size of the inlet piping is the same as, or greater
than, the nominal size of the valve inlet flange; and in which the length does
not exceed the face-to-face dimensions of a standard tee of the required
pressure class.
Do not locate POSRV inlets where excessive turbulence is present, such as
near elbows, tees, bends, orifice plates or throttling valves.
Section VIII of the ASME Boiler and Pressure Vessel Code requires the
inlet connection design to consider stress conditions during valve operation,
caused by external loading, vibration, and loads due to thermal expansion of
the discharge piping.
The determination of reaction forces during valve discharge is the
responsibility of the vessel and/or piping designer. Baker Hughes publishes
certain technical information about reaction forces under various fluid flow
conditions, but assumes no liability for the calculations and design of the

inlet piping.

External loading, by poorly designed discharge piping and support systems,
and forced alignment of discharge piping can cause excessive stresses and
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Prevent dirt from
entering outlet or inlet
port.
Always install valve
in a vertical, upright
position.
Decontaminate or
clean if necessary
before pretesting or
disassembly. Safety
and environmental
precautions must
be taken for the
decontamination or
cleaning method used.
Consolidated 4900 MPV Series POSRV Manual
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