3. OPERATION
Page 17
© 2007 DH Instruments, a Fluke Company
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3.1
OPERATING PRINCIPLE
Numerical references in this section refer to Section 3.1, Figure 6.
GPC1 is a self-contained system designed to set and adjust gas pressure into static pressure test and
calibration systems. GPC1-16000 operates from atmosphere (zero gauge) to 110 MPa (16 000 psi).
GPC1-10000 operates to 70 MPa (10 000 psi). GPC1 combines the capability to execute large pressure
changes very quickly with very fine pressure adjustment.
GPC1 uses two different techniques to set and adjust pressure. These are rough pressure control using
the TEST INLET valve (12) and TEST OUTLET valve (15) and fine pressure control using the PDVV (+)
(13) and (-) valves (14).
The first means of generating and adjusting pressure uses the external gas pressure supply (1) with the
TEST INLET SET regulator (5), TEST INLET valve (12) and TEST OUTLET valve (15). This combination
is used for filling the system under test, making large pressure changes and for rough pressure control.
The valves are Belleville spring loaded, half-turn needle valves. Their operation is highly progressive
over a half-turn with mechanical stops at each end so they cannot be over tightened. The regulator is self
venting and its output is indicated by the TEST INLET gauge (4). The valve is turned clockwise (CW) to
close and counter-clockwise (CCW) to open. A WHITE dot on the handle body indicates the valve’s
current open/close position. The TEST INLET SET regulator (5) and TEST INLET gauge (4) are used to
set the supply pressure to the TEST INLET valve (12). Opening the INLET valve (12) allows the supply
pressure to enter GPC1 and reach the TEST ports (6,7,8). Opening the OUTLET valve (15) exhausts
gas, reducing pressure in the system.
The second means of generating and adjusting pressure is the Pneumatically Driven Variable Volume
(PDVV) (16) combined with the PDVV (+) (13) and (-) valves (14). This combination is used for smaller
pressure changes and fine pressure control. The PDVV is a pneumatically actuated variable volume. A
piston or plunger in a cylinder is exposed to the high pressure gas to be adjusted.
The other end of the plunger is connected to a dome loaded pneumatic actuator. Changing the
pneumatic pressure on the dome loaded actuator causes the plunger to move, increasing or decreasing
the high gas pressure. A spring returns the plunger to its minimum stroke position when there is no
pressure on the dome. A mechanical system tracks movement of the plunger and an indicator (18)
displays the plunger position on the front panel. The PDVV (+) (13) and (-) valves (14) are momentary,
poppet valves that open when pressed. The (+) valves (13) admit drive air pressure to the PDVV
actuator causing the PDVV piston to move forward, compressing the high pressure gas and increasing
the pressure. The (-) valves (14) have the opposite effect, causing pressure to decrease when they are
operated.
