Information on testing vacuum continued – Just Better Keeping the life of your pump User Manual

Page 4

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Information on Testing Vacuum Continued

First, let’s look at the construction of JB’s isolation valve (Figure 14). This fi g-
ure shows the isolation valve in the closed position. The brass ball is sandwiched
between two Tefl on seals, making a positive seal, with a solid brass surface
blocking access to the intake chamber. The adapter nut on the top, outside of the
pump, is where the intake fi tting is connected. It is sealed with Loctite and an o-
ring. If this nut has not been disturbed, the chances of a leak are very minimal.
The stem has a dual o-ring seal and, even if this leaked, with the isolation valve
in the closed position there would be no effect on holding a vacuum. A leak at
the stem would effect the depth of vacuum the pump could achieve.

Adapter nut w/ o-ring

Teflon seals (2 each)

Retainer Plug w/ o-ring

Poly Ball 7/16”
(oil check system)

Brass isolation ball

Retainer ring

Stem w/ o-ring

Figure 14

With a micron gauge connected directly to the intake of the pump and vacuumed
to 50 microns, closing the isolation valve will result in a rapid rise in pressure,
almost to atmosphere. Look closely at the area around the isolation valve. Even
though small, air is trapped in this area. When we begin to close the isolation
valve, there is a position of the ball that allows this trapped air to enter the vacu-
um being created. On a large system, this small amount of air would not create
a conspicuous change in microns. However, with almost no volume, the sudden
introduction of air to this direct hook-up is obvious and would be displayed on
a micron gauge. Refer to the previous page for the isolation valve positions.
When the isolation valve is put in the pause position, this gives the cartridge
(the pumping mechanism) access to the air trapped in this area and within a few
seconds, that trapped air is removed.

Moving to the connections on the pump, the factory intake is loctited into place
and each pump is tested for leaks. If this is not disturbed, the chances of a leak

are virtually non-existent. Any leak would
come from the connection at the port being
used and to the connection to the system.
One of the most common errors with both
the o-ring and the gasket couplers is the
wrenching down of these couplers with
a pair of pliers or channel locks (Figure
15). Please refer to our “Principles of Deep
Vacuum” article. This article can be found
on JB’s website under tech-
nical information/ troubleshooting. Or type les/fi le/
Deep_Vacuum.pdf into your web browser to
take you directly to the page.

Deep Vacuum

O-Ring Coupler Cut-Away







O-Ring in





As this article shows, there is a need for
sealing with a vacuum tight o-ring (Figure
16). Gaskets, like those used in charging
lines, are made for pressure. What wrench-
ing of the coupler does is to smash the brass
cup that holds the gasket or o-ring against
the male fl are fi tting. This causes the brass
cup to expand outward against the threads of
the coupler and makes it tight to turn. This
causes the o-ring to fall out of the cup that is
holding the o-ring or gasket in place.

Figure 15


Figure 16

Figure 17

Another error that we see is that technicians
have a brass adapter fi tting on the intake of the
pump with no copper gasket. The fi rst time you
wrench the adapter into place, it might seal.
But, as soon as you break the seal and retighten,
there is a chance for a leak. The best hook-up
that guarantees there are no leaks in the system
is by using JB’s DV-29. This hook-up is
depicted in Figure 17. The DV-29 consists of a
fl exible metal hose, ball valve with depressor, a
90° male fl are with coupler, and valve assembly
with male connections. The hook-up and parts
are depicted in JB’s catalog, version 42 on page

Charging lines have been used for many years
for the vacuum end of air conditioning and
refrigeration servicing. Charging line use