Ashcroft LD - Differential Pressure Switches User Manual

Page 2

SETPOINT ADJUSTMENTS
Setpoints are changed by means of the setpoint adjusters. The
LD-S single switch has one adjuster and the LD-A adjustable
deadband and LD-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 LD-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 monitored
light goes off). If setpoint is on decreasing differential pressure,
turn adjuster so that switch resets (if common – normally closed
circuit is being monitored light comes on). When the setpoint
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.

Installation and Maintenance Instructions
for ASHCROFT

L-Series Snap Action

Switches for Differential Pressure Control

SERIES LD-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 verification under Series LD-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 oper-
ates 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 LD-A ADJUSTABLE DEADBAND SWITCH
Remove cover. Adjuster “B” controls the operating point of the
switch on increasing pressure. Adjuster “A” controls the re-set-
point 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.

Intermittent operation up to proof pressure is permissible, how-
ever, some change of setpoint may be noted.

Operation and correct setpoint actuation should be routinely
tested.

© 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&M009-10016-10/00 (250-2871) AMR 12/07