FD151 Gas Compressor 7
arrangement for your machine. If the valve/unloader
number for your machine is 3 or 4, proceed to
chapter 2 (your machine has no unloaders).
The suction valve unloader is a small piston and
cylinder assembly that is installed over the suction
valve (see Figure 1.1A). The small piston is connected
to a rod that extends into the suction valve assembly.
The unloader piston is depressed when gas
pressurized to 40 psi or more above suction pressure
is injected into the unloader cylinder.
In the depressed position, the piston pushes the rod
against the suction valve disk to hold the suction
valve in an open position. In this position, no
compression will occur, even though the pistons are
still moving up and down.
The unloaders are controlled by devices which
control the flow of gas into and out of the unloader
cylinder. The different types of unloader controls may
be summarized as follows:
SPECIFICATION 9 - When the gas being
compressed cannot be vented to the atmosphere,
electronic controls should be used as shown in
Figure 1.7D. The use of an optional three-way
solenoid valve allows gas from the unloader to be
vented back to the compressor suction instead of to
atmosphere. A time delay may be used to achieve
loadless start and a pressure switch may be used
to achieve constant-speed unloading.
Specification 9
Figure 1.7D
Unloaded
Loaded
