Ashcroft GD - Differential Pressure Switches User Manual

Page 2

SETPOINT ADJUSTMENTS
Setpoints are changed by means of the setpoint adjusters. The
GD-S single switch has one adjuster and the GD-A adjustable
deadband and GD-D dual switches each have two adjusters. On
switches with two adjusters, the one on the left is referred to as
“A” and the right one is referred to as “B”; see illustration.
Setpoints can be adjusted from 20 to 100 percent of full range
on increasing pressure.

SERIES GD-S SINGLE SWITCH
Remove cover. For setpoint adjustment on either increasing or
decreasing pressure to within ±1% of nominal range, mount the
switch on a calibration stand and use a suitable reference such
as an ASHCROFT

Duragauge or test gauge. Monitor switch

with a light or meter.

Apply Low pressure. Then apply High pressure equal to the

low pressure plus the differential pressure setpoint. If setpoint is
on increasing differential pressure, turn adjuster so that switch
operates (if common – normally closed circuit is being moni-
tored light goes off). If setpoint is on decreasing differential pres-
sure, turn adjuster so that switch resets (if common – normally
closed circuit is being monitored light comes on). When the set-
point has been achieved, raise and lower the high pressure to
ensure that the setpoint is correct.

The deadband (difference between the operate and reset

pressures) may be verified at this time to be between the values
noted on the nameplate label.

SERIES GD-D DUAL SWITCH
Remove cover. For setpoint adjustment to within ±1% of nominal
range, mount the switch on a calibration stand and use the suit-
able reference such as an ASHCROFT

Duragauge or test

gauge. Monitor switch with a light or meter.

Apply Low pressure. Then apply High pressure to the higher

of the two required setpoints. Turn adjuster “B” until the switch
operates or resets as required. See discussion of increasing or
decreasing differential pressure setpoints and deadband verifi-
cation under Series GD-S Single Switch. When the setpoint has
been achieved, raise and lower the High pressure. Then reduce
the High pressure to the lower setpoint differential pressure and
turn adjuster “A” until the switch operates or resets as required.
Verify this setpoint by raising and lowering the High pressure.
Now increase the High pressure to the higher setpoint and
make final adjustment on “B.”

SERIES GD-A ADJUSTABLE DEADBAND SWITCH
Remove cover. Adjuster “B” controls the operating point of the
switch on increasing pressure. Adjuster “A” controls the re-setpoint
of the switch on decreasing pressure.

For accurate setpoint adjustment, mount the switch on a cali-

bration stand and use a suitable reference such as an
ASHCROFT

Duragauge or test gauge. Monitor switch with a

light or meter. Apply Low pressure. Then apply High pressure to
the required setpoint pressure.

Turn adjuster “B” until switch operates. Then lower differential

pressure to the re-setpoint and turn adjuster “A” until the switch
resets. Now increase pressure to the operating point and make
final adjustment on “B.” Raise and lower pressure to ensure that
the setpoint and re-setpoint are correct.

SOME PRECAUTIONS TO OBSERVE
Do not loosen the screws holding the precision switch element(s)
or mounting bracket in place.

Nameplate PROOF pressure should not be exceeded. Inter-

mittent operation up to proof pressure is permissible, however,
some change of setpoint may be noted.

Operation and correct setpoint actuation should be

routinely tested.

Installation and Maintenance Instructions
for ASHCROFT

G-Series Snap Action

Switches for Differential Pressure Control

© 2007 Ashcroft Inc., 250 East Main Street, Stratford, CT 06614-5145, USA, Tel: 203-378-8281, Fax: 203-385-0499, www.ashcroft.com
All sales subject to standard terms and conditions of sale. I&M009/10020-10/00 (250-2892) AMR 12/07