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Technical Instructions
Document Number 155-027P25
February 14, 2005
Troubleshooting
Control Pressure
Remains at 1/2 psig
Control Pressure
Remains at Maximum
(15—25 psig)
Excessive Air Leakage
from Nozzle-Control
Pressure Does Not
Drop
Replacement of
Membrane Element
Page 6
Troubleshooting contains the most common problems and solutions.
1. Remove the cover and connect a pressure gauge.
2. Gently press the nozzle lever against nozzle. The control pressure should increase. If
not, the restrictor hole in the restrictor plate (6) is clogged.
3. Replace the restrictor plate using the replacement parts in the Restrictor Plate Kit.
See Table 2.
4. Remove the old gaskets (5 and 7) and restrictor plate (6). Reassemble with the new
kit parts, putting them in the same relative positions as the original parts. Make sure
that the gasket connecting the two holes is between the restrictor plate and the
cover.
1. Gently push the nozzle lever (2) away from nozzle (17).
2. If the control pressure does not drop to approximately 1/2 psig, check for a clogged
nozzle.
3. Carefully clean the tip of the nozzle. Also clean the nozzle lever where it contacts the
nozzle, as dirt will accumulate and clog the nozzle opening.
1. If excessive air leakage occurs and the control pressure does not drop to 1/2 psig
when the nozzle lever is pulled away from the nozzle, then there is dirt on one of the
relay ball valves. See Figure 4 in the Operation section.
2. The dirt particle on either the supply or the exhaust balls can usually be removed by
moving the lever so that it alternately opens and closes the nozzle. This fluttering
action will usually dislodge dirt from the ball valves.
3. Disassembly of the body (19) and base (20) to access the relay is not recommended.
1. If the membrane element (13) is damaged and becomes cracked or torn, replace it
with parts in the Membrane Element Kit. See Table 2.
2. Disconnect the old element by removing screws (12) and (16).
3. Attach the new element.
4. Recalibrate using the procedure in the Calibration section.
HU 186 Room and Duct Hygrostats
Siemens Industry, Inc.
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