Groth 1721B - Manual (Page 7)

Page 7 of 18
DISASSEMBLY
WEIGHT LOADED PALLET ASSEMBLY
1. Loosen and remove all hex nuts and washers.
2. Remove the vent cover or weatherhood from the valve body.
3. Remove the pallet assembly by firmly grasping the stem and lifting up. Depending on the pressure/vacuum settings of the
particular valve, weight plates may have been added to the pallet assembly. The weights and pallets must be reinstalled in
their original locations. Make sure that all weight plates stay with the appropriate pallet assembly. If working with more than
one valve tag the assemblies as they are removed from the valves.
4. Carefully inspect all guides for corrosion, damage or product build up. Also inspect the guide hole in the vacuum cover. Check
the metal seating surfaces for pitting or build up. It is recommended to replace all soft goods including diaphragm, O-Ring
(for machined pallets, Figure 2) and cover gasket.
TABLE 6: STEM LENGTH - IN [mm]
Valve Port (valve type)
Valve
Size
Pressure Port Vacuum Port
In [mm] Spring-Loaded Hollow-Stem Weight-Loaded Spring-Loaded Hollow-Stem Weight-Loaded
2" [50] 8.50 [215.9] 6.00 [152.4] 6.81 [172.97] 8.50 [215.9] 3.88 [98.55] 4.63 [117.6]
3" [80] 10.80 [274.3] -- 7.81 [198.37] 10.80 [274.3] -- 5.50 [139.7]
4" [100] 13.00 [330.2] 7.88 [200.15] 8.63 [219.2] 13.00 [330.2] -- 5.50 [139.7]
TABLE 7: RECOMMENDED PALLET
ASSEMBLY TORQUE
STEM THREAD
SIZE
PALLET ASSEMBLY
TORQUE
REQUIREMENT FT-LBS
[N-m]
METALLIC STEM
(ALUMINUM /
STAINLESS STEEL)
¼” 4 [5.4]
3/8” 16 [21.7]
NOTE: If the seat is damaged it must be lapped using a ground flat metal disc and a fine grit emery cloth attached to the disc.
Wipe seating surface clean before proceeding.
Figure 2 - Pallet Assembly Detail
5. Prior to final assembly, verify that the pallet and weights are back in their proper location. Assemble in reverse order. Make
sure that pallet assembly is flat on the seat and that the stem is not cocked when the cover is installed. Oil, grease or other
lubricant are not required on guides or other metal surfaces of valves, and can hinder free movement. If the valve is in high
temperature service or stainless steel external fasteners are used, apply an anti-seize compound such as moly-disulfide to
all threaded components. Tighten all hex nuts firmly.