Changing Proportional, Reset, Or Differential Relief Valve; Testing Relay Dead Band; Changing Relay; Replacing Bellows - Emerson Fisher 2502 Instruction Manual

Instruction Manual
D200126X012
5. Install and tighten the bearing assembly (key 12, figure 14) in the case (key 1, figure 14). Secure the operating arm
base or pointer assembly to the rotary shaft by tightening the hex nut (key 40, figure 14). Connect the supply and
output pressure tubing and perform the calibration procedure.

Changing Proportional, Reset, or Differential Relief Valve

1. Remove the proportional band valve assembly (key 36, figure 14) by unscrewing it from the relay base (key 23,
figure 14). Install the desired replacement assembly, or a 1/8 NPT pipe plug into the proportional band tapping if

testing relay dead band.

2. To change the reset restriction valve assembly (key 91), remove the two mounting screws (key 182) located on the
back side of case. Install the replacement valve assembly, and reconnect the tubing connections.
3. Remove the differential relief valve assembly (key 186, figure 14) by removing the two mounting screws (figure 9)
that anchor the valve to the manifold (key 184, figure 14). Install the valve with the arrow pointing to the same
letter(s) as before removal, unless it is desired to change the relief action.
Testing Relay Dead Band
1. Replace the proportional band adjustment assembly with a 1/8 NPT pipe plug according to the Changing
Proportional, Reset, or Differential Relief Valve section.
2. Turn on the supply pressure and set it to 1.4 or 2.4 bar (20 or 35 psig).
3. By changing the process variable and adjusting the RAISE LEVEL control, set the output pressure to 1.0 or 2.0 bar
(15 or 30 psig). While monitoring the output pressure, slowly change the process until an output pressure change
can just be detected, and record the value of the process variable at the detection point.
4. Change the process variable in the opposite direction until another output pressure change can be detected, and
again record the value of the process variable. If the difference between the two recorded values (the dead band) is
more than 0.2 percent of the maximum displacer length, the relay will have to be replaced or repaired according to
the Changing Relay and the Disassembling Relay sections.
5. Turn off the supply pressure, remove the pipe plug, and install the proportional band adjustment assembly.

Changing Relay

The relay may be removed for cleaning or replacement, and must be taken off to remove the lower bellows.
1. On a controller with indicator assembly, loosen the two lower screws of the relay case and slide out the indicator
base plate (key 53, figure 14).
2. Disconnect the tubing (key 11, figure 14) from the relay.
3. Remove both mounting screws, the relay, and the relay gasket (keys 43, 34, and 22, figure 14).
4. Install a new gasket, the replacement relay if necessary, and both mounting screws. Reconnect the tubing. On a
controller with indicator assembly, slide the base plate under the two lower screws of the relay case, align the plate
so that the pointer will read properly, and tighten the screws.

Replacing Bellows

Key numbers are shown in figure 14.
1. To gain access to the lower bellows, remove the relay according to the Changing Relay section.
2. Remove the upper and lower bellows frame screws (key 96) that hold both bellows assemblies to the bellows frame.
Unscrew each bellows from the spacer (key 98), being careful not to lose the O‐ring (key 57, not shown) from the
spacer end of the bellows.
3. Inspect each bellows and O‐ring and replace if necessary, using an unpainted bellows for a 0.2 to 1.0 bar (3 to 15
psig) range and a red bellows for a 0.4 to 2.0 bar (6 to 30 psig) range. Be sure to install the O‐ring at the spacer end
of the bellows.
2502 Controllers
June 2017
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