Operation and Adjustment cont’d
The CVS Controls nameplate indicates a “bench
set” pressure range in addition to a standard
diaphragm pressure range. The “bench set”
pressure range indicates the range required to
completely stroke the valve with out any pressure
in the valve body, for example as if the valve
were being tested on the work bench. While In
service, however, with the specified pressure
drop applied across the valve, it should stroke
over the standard diaphragm pressure range as
indicated on the nameplate.
Once the control valve has been installed and
connected to the controller, it should be tested for
correct travel, lack of friction and correct action
(air-to-open or air-to-close) to match the
controlling instrument. To ensure the most
effective operation, the actuator stem and the
valve plug stem must move freely when
responding to the loading pressure change on
the diaphragm.
Disassembly Instructions
Although the following instructions describe how
the CVS Type 657 Diaphragm Actuator can be
completely disassembled, when inspection or
repairs are required, only disassemble those
parts required to accomplish the job.
Consult Figure 4, and proceed as follows for
disassembly:
1. Bypass the control valve and exhaust any
actuator loading pressure to atmospheric.
Disconnect the actuator supply line and any
leakoff piping.
2. Relieve all pressure from the spring by
threading the spring adjuster (key 2) out of
the yoke.
3. To remove the valve body from the actuator,
separate the stem connector (key 21) and
remove the yoke locknut.
4. Loosen the stem locknuts (keys 13 and 14),
remove the two cap screws and separate the
stem connector.
5. Loosen the diaphragm case cap screws and
nuts (keys 19 and 20) and remove the upper
diaphragm case.
6. Remove the molded diaphragm (key 6).
7. Extract the diaphragm plate and actuator
stem (keys 5 and 3) as an assembly. These
parts can be further separated if required.
8. Remove the actuator spring (key 1) and
9. If necessary, remove the lower half of the
diaphragm case (key 8) by loosening the cap
screws.
10. Removing the spring adjuster will complete the
disassembly.
Assembly Instructions
1. The CVS Type 657 Actuator can be assembled in
the reverse order of the disassembly instructions.
These additional steps below will assist with
proper assembly and continued operation.
2. Apply lubricant to the threads and spring seat
bearing surface of the spring adjuster (See
location marked “LP” on Figure 4).
3. Ensure that the spring seats and the lower seat
align properly and rest against the diaphragm
plate.
4. Use a criss-cross pattern to evenly tighten the
nuts on the casing bolts.
5. If the stem locknuts were removed during
disassembly, install them onto the valve plug
stem and place the travel indicator (key 12) with
the cupped side downward.
6. Secure the actuator onto the valve body using
the yoke locknut.
7. Assemble the stem connection as follows
according to the required action:
a. Mounted on Body with “Push Down to
Close” Valve Plug
i. When the body is assembled and the
actuator is mounted, ensure the valve
plug is in the closed position.
ii. Once the locknuts are secured onto the
stem, set the travel indicator disc onto
the locknuts with the cupped portion
facing downward.
iii. Raise the valve plug off of the seat, with
the travel specified on the nameplate, or,
pressure the actuator until the stem
moves down the specified valve travel.
iv. Install the stem connector by clamping
the actuator stem to the valve stem.
v. Raise the indicator disc to the stem
connector, using the locknuts to tighten
in position.
vi. Ensure that the desired total travel is
available by cycling the actuator. This
will also demonstrate that the valve plug
seats properly. If necessary, minor travel
adjustments can be made by slightly
loosening the stem connector, tightening
the locknuts and screwing the stem
either into or out of the stem connector
using a wrench on the locknuts.
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