Groth 1720A - Manual (Page 6)

6
MAINTENANCE:
Groth Corporation recommends that all
service performed on a pressure/vacuum
relief valve be done at the factory or a factory
authorized repair center. Trained mechanics
with specialized test equipment will ensure
that the valve is accurately set.
It is important to regularly inspect the
diaphragm, guides and seating surfaces to
ensure the valve can open freely. Refer to
Fig. 4 on the next page that illustrates a
typical Pressure/Vacuum relief valve when
disassembling the unit.
WARNING: Before disassembling valve
carefully read and understand the Safety
Warnings listed on page 3.
1. Loosen and remove all nuts (#1).
2. Lift off the pressure (#2) and vacuum (#3)
covers.
3. Remove the vacuum and pressure pallet
assemblies by firmly grasping the stems (#4 &
#5) and lifting up. Depending on the
pressure/vacuum settings of the particular
valve, weight plates may have been added to
the pallet assemblies. The weights and
pallets must be reinstalled in their original
locations. Make sure that all weight plates
stay with the appropriate pallet assembly.
Tag the assemblies "Pressure" and "Vacuum"
as they are removed from the valve.
4. Carefully inspect all guides (#6 & #7) for
corrosion, damage or product build up. Also
inspect the guide hole in the pressure (#2)
and vacuum (#3) covers. Check the metal
seating surfaces for pitting, corrosion or
product build up. It is recommended to
replace all soft goods including diaphragms
(#8 & #9), O-Ring (#10) and cover gasket
(#11). For a list of recommended spare parts
see Table 4.
NOTE: If the seats are damaged they must
be lapped using a perfectly flat ground metal
disc and fine grit lapping compound attached
to the disc. Wipe the seating surface clean
before proceeding.
5. If the stems are being replaced, check
Table 3 to ensure that the correct length is
being used in both the pressure and vacuum
ports.
TABLE 3 - Stem Length - In. (cm)
Valve Valve Model
Size Pressure Vacuum
[In] Port Port
2 6.81
(17.3)
4.63
(11.8)
3 7.81
(19.8)
5.50
(14.0)
4 8.63
(21.9)
5.50
(14.0)
6. Verify that the pallets and weights are
back in their proper location. Assemble in
reverse order, observing the maximum
dimensions for the weight blocks as listed in
Table 7 on Page 8. Make sure that pallet
assemblies sit flat on the seat and that the
stem is not cocked when the pressure (#2)
and vacuum (#3) covers are installed.
Tighten all nuts (#1) firmly.
WARNING : When assembling a P/V valve,
always use the correct length stem (as specified
in Table 3), put the pressure and vacuum pallet
assemblies back in their original location and
ensure that the stem is straight and fits into the
guide in the cover.
1. If the stem length is too long, pallet lift will be
restricted and the valve will not attain its full
rated flow capacity.
2. If the pressure and vacuum pallet assemblies
are mixed at assembly, the settings will be
changed.
If the stem is cocked at an angle, pallet lift may be
completely blocked. An over-pressure can occur
if any of these three conditions happens. This
can cause a tank failure, severe personal injury
and material damage.