DWYER INSTRUMENTS, INC.
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.
Phone: 219/879-8000
Fax: 219/872-9057
www.dwyer-inst.com
e-mail: [email protected]
INSTALLATION
1. Select a location that is free from excessive vibration, corrosive atmosphere and
where the ambient temperature is within the limits for these switches.
2. Mount standard switches with the diaphragm in a vertical plane and with switch
lettering and nameplate in an upright position. Some switches are position
sensitive and may not reset properly unless they are mounted with the diaphragm
vertical. (Special units can be furnished for other than vertical mounting
arrangements if required.)
3. Connect switch to source of pressure, vacuum or differential pressure. Metal tubing
with 1/4˝ O.D. is recommended, but any tubing which will not restrict the air flow
can be used. Connect to the two 1/8˝ female NPT pressure ports as noted below:
• Differential pressures - connect pipes or tubes from source of greater pressure
to high pressure port marked HI-PR and from source of lower pressure to low
pressure port marked LO-PR.
• Pressure only (above atmospheric) - connect tube from source of pressure to
high pressure port. The low pressure port is left open to atmosphere.
• Vacuum only (below atmospheric pressure) - connect tube from source of
vacuum to low pressure port. The high pressure port is left open to atmosphere.
4. Electrical connections to the standard single pole, double throw snap switch are
provided by means of screw terminals marked “common”, “norm open”, and “norm
closed”. The normally open contacts close and the normally closed contacts open
when pressure increases beyond the set point.
5. Switch loads should not exceed the maximum specified current rating of 15 amps
resistive. Switch capabilities decrease with high load inductance or rapid cycle
rates. Whenever an application involves either of these factors, the user may find
it desirable to limit the switched current to 10 amps or less in the interest of
prolonging switch life.
OPERATION
Pressure acting on the power diaphragm rotates the amplifying lever, which in turn
extends the range spring and rotates the snap switch input lever. When the set point
is reached, the snap switcch is actuated and the electrical contacts make or break.
ADJUSTMENT
To change the set point, proceed as follows:
A. Remove the snap-on cover from the conduit enclosure by loosening its retaining
screw and pulling firmly at its bottom end. Turn the slotted adjustment screw at
the top of range spring housing clockwise to raise the set point pressure and
counter-clockwise to lower the set point.
B. The recommended procedure for calibrating or checking calibration is to use a
“T” assembly with three rubber tubing leads, all as short as possible and the
entire assembly offering minimum flow restriction. Run one lead to the pressure
switch, another to the manometer of known accuracy and appropriate range, and
apply pressure through the third tube. Make final approach to the set point very
slowly. Note that manometer and pressure switch will have different response
times due to different internal volumes, lengths of tubing, fluid drainage etc. Be
certain the switch is checked in the position it will assume in use, i.e. with
diaphragm in a vertical plane and switch lettering and nameplate in an upright
position.
C. For highly critical applications it is a good idea to check the set point adjustment
and reset it as necessary once or twice in the first few months of operation. This
will compensate for any change in initial tension which may occur in the spring
and diaphragm. For most applications this change will not be significant and no
resetting will be required.
MAINTENANCE
Moving parts of these switches are sealed in and are permanently tamper proof. The
single adjustment is that of the set point. Care should be taken to keep the switch
reasonably dry and free from dust or dirt. No lubrication or unusual precautions are
required for normal use.
Power must be off while wiring connections are being made.
CAUTION
Do not exceed the specified voltage rating. Permanent damage
not covered by warranty may result.
CAUTION
