MPC1-1000 and MPC1-3000 User’s Manual
© 2001 - 2007
DH Instruments, a Fluke Company
Page 18
5.2.3
PRESSURE INCREASE LEAK (BELOW ATMOSPHERE)
This type of leak is similar to Section 5.2.2 and can be caused by the same components
and fittings. However, it is much more difficult to locate since it is not possible to use leak
detection fluid. It is often useful to pressurize the system above atmosphere and find the leak
using the procedures outlined in Section 5.2.2 since a vacuum leak can often be found under
pressure conditions. However, sometimes a leak under vacuum conditions does not exist
under positive pressure conditions.
If the leak cannot be found with a positive pressure, it is recommended the MPC1 be
returned to
DHI
for repair. If it cannot be returned, proceed as outlined below.
First, isolate the leak to a particular area within the MPC1. Establish the conditions under
which the leak occurs. Then close the test outlet valve, position the outlet selection valve to
VACUUM and open the equalization valve (pull out). Wait for the pressure to stabilize (about
1 to 2 minutes). Close the equalization valve (push in). If the leak is gone, go to Step
n
.
If the leak is still present, go to Step
o
.
n
If the pressure drop is gone, the leak is between the equalization valve stem seal and the
test outlet valve. Possible sources include the low pressure side of the VV, low pressure
side of the equalization valve and/or the fittings between the two valves.
Remove the top cover. Remove the connecting tube between the equalization valve and
the test outlet valve. Inspect the fittings and tube ends for damage. Replace any
damaged parts and reassemble. Check for leaks. If the leak is still present, return the
MPC1 for repair.
o
Most leaks are located in either the VV, gauge, filter and/or in the connecting tubing
including between the test inlet and equalization valve. Remove the top cover.
Disconnect the gauge tube at the tee located near the test port and plug the tee (refer to
Section 6.1). Repeat the leak check. If the leak is gone, the leak is in the gauge or the
disconnected fitting. Replace the fitting and/or repair or replace the gauge.
Check all the fittings within the suspected circuit by disconnecting and inspecting them.
Replace any damaged fittings. Reassemble and leak check. If the leak is still present,
return the MPC1 to
DHI
Technical Service for repair.
