The gas handling and controls systems have been designed to prevent excessive pressure build up in the system in order to protect the target cells from rupture.
In the event that the pressure in the system begins to rise there are multiple
vent paths to release it. The first line of defense is the recovery tank.
The second line of defense is a small orifice solenoid valve
which is slaved to a pressure transducer. This valve, CSV28 for H
and
CSV57 for D,
is normally controlled by the limit
output of the computer (via a VME based relay) readout of
the pressure transducer that views the target
relief line, PT131 for H and PT140 for D. The valve itself is mounted
in the fill line relief assembly. The separation of the valve from its
controlling pressure gauge should provide some dampening of the response
and the small orifice of the valve also ensures that it will
be able to make pressure adjustments gently if need be.
There is
a separate relief valve on the fill side of the target, CRV30 for H and
CRV59 for D. This relief is mounted in parallel with the small orifice
solenoid valve. Right on top of the cryocan, on the return side of the target,
there is a large size (one 
) relief valve.
All target pressure reliefs are connected to the
nitrogen vent line of the Hall A superconducting magnets.
This is a 3.5 diameter
copper pipe which is filled with nitrogen gas at atmospheric pressure.
Thus any vented target gas is placed in an inert environment until it is
released outside of Hall A. Each gas tank has one relief valve and one rupture
disk (CRV43 and CRD44 for hydrogen, and CRV72 and CRD143 for deuterium).
In addition to the reliefs on the gas handling system described above, the
scattering chamber itself has a four- one PSIG relief, VRV01.
This is the path that the
hydrogen will take in the event of a cell failure.
The target pressure reliefs are summarized in Table 3.2.