Murphy A20P & A25P Series Pressure Swichgage Instrument
The A20 Series (2 inch/51 mm dial) and the A25 Series (2-1/2 inch/64 mm dial) Swichgage? instruments are diaphragm-actuated, pressure-indicating gages, with built-in electrical switches for tripping alarms and/or shutdown devices.
Features:
Corrosion resistant polycarbonate case
Indicating gage and limit switch
Switch can activate alarms and/or shut down equipment
Critical pressure limit switch is visible and adjustable (most models)
Contact(s) isolated from ground
FW Murphy A20 and A25 Series Pressure Swichgage. instrument
A20 Series A25 Series
2 and 2-1/2 in. (51 and 64 mm) Dial
■ Corrosion Resistant Polycarbonate Case
■ Indicating Gage and Limit Switch
■ Switch Can Activate Alarms and/or Shut Down Equipment
■ Critical Pressure Limit Switch Is Visible and Adjustable (Most Models)
■ Contact(s) Isolated From Ground
Description
The A20 Series (2 inch/51 mm dial) and the A25 Series (2-1/2 inch/64 mm dial) Swichgage instruments are diaphragm-actuated, pressure-indicating gages, with built-in electrical switches for tripping
alarms and/or shutdown devices.
Ranges are available from 0-15 psi (103 kPa) [1.0 bar] thru 0-400 psi (2.8 MPa) [28 bar].All models of these rugged, built-to-last instruments
are face sealed from the environment by the unique combination of a polycarbonate case and lens, a polished stainless steel bezel and O-ring
seals. Ranges above 30 psi (207 kPa) [2 bar] are totally sealed from the external environment (except PE Series).
Accuracy and protection from moderate overpressure is assured by a unique, unitized diaphragm chamber. A built-in pulsation dampener helps eliminate
pointer flutter and is removable for cleaning. For series A20P and A25P, the gage pointer acts as a pressure indicator and as one switch pole which
completes a circuit when it touches the adjustable limit contact. Contacts have self-cleaning motion to ensure electrical continuity.
Models A20PE and A25PE have internal snap-acting SPDT switches for three wire control; can be wired to make or to break a circuit.
Gage-only models, without switches (Murphygage instrument) are also available.
Applications
A20/A25 Series applications include: engines/equipment in Oil Field, Marine, Irrigation, Construction and Trucking Engines for Lube Oil Pressure, Water
Pump Pressure, Hydraulic Pressure, Air Pressure, etc.
Specifications
Dial: White on black, dual scale; U.S.A. standard scale is psi/kPa; U.K. standard scale is psi/bar (see How to Order).
Case: Polycarbonate/glass filled, corrosion-resistant;
steel mounting clamp included.
Bezel: Polished stainless steel, standard; others are
available (see How to Order).
Pointer: Tempered nickel silver; Red tip.
Lens: Polycarbonate, high-impact.
Oil: Silicon Oil.
Temperature Range:
Ambient: -40°F (-40°C) thru 150°F (66°C).
Process: -40°F (-40°C) thru 250°F (121°C).
Process Connection: 1/8-27 NPTM brass.
Sensing Element: Beryllium copper diaphragm.
Gage Accuracy (% of Full Scale):
RANGE LOWER 1/4 MIDDLE 1/2 UPPER 1/4
≤300 psi (20 Bar) ±3% ±2% ±3%
400 psi (28 Bar) ±3% ±3% ±5%
Maximum Pressure: See Pressure Ranges and
Factory Settings table on page 2.
Adjustable Limit Contact (A20P and A25P):
SPST contact; pilot-duty only, 2A@30 VAC/DC; Closed when the low limit is met. Open when pointer is in normal operating range.
Contacts are gold flashed silver. Limit Contact Adjustment: by a 1/16 in. hex
wrench thru 100% of the scale. Wiring: A20P: Number 4 screw terminals; A25P: Number 6 screw terminals.
Snap-Switch Rating (A20PE and A25PE):
SPDT, 3 A@ 30 VDC inductive; 4 A @
125 VAC inductive.
Wiring: A20PE: Number 4 screw terminals;
A25PE: Number 6 screw terminals.
Unit Weight: A20 Series: 8 oz. (0.23 kg).
A25 Series Models: 11 oz. (0.31 kg).
Unit Dimensions: A20 Series: 3 x 3 x 3 in. (76 x
76 x 76 mm). A25 Series Models: 4-3/4 x 4-3/4
x 2-3/4 in. (121 x 121 x 70 mm).
Base Models
A20P and A25P Series Swichgage
The gage pointer makes with an adjustable contact to complete a pilot-duty circuit.
A20PE and A25PE Swichgage
A20PE (was A20EO) and A25PE (was A25PEO).
Features internal snap-acting SPDT switches, instead of the single pole/pointer contacts. When the switch closes on falling pressure, it becomes
Set, as pressure rises the switch Resets (refer to wiring diagram on page 3). Model A25PE is CSA listed for non-hazardous areas.
Model A25PE-EX is CSA listed for Class I, Division 1, Groups C and D hazardous areas.
A20PABS and A25PABS Swichgage
instrument
Sames as A20P and A25P with internal SPDT
snap-switch for pre-alarm.
A20PG and A25PG Murphygage
instrument
Gage without contact(s).
**Products covered by this bulletin comply with EMC Council
directive 89/336/EEC regarding electromagnetic compatibility
except as noted.
AP-94030B page 1 of 4
Dimensions
A20 Series Models
2-1/4 in. 2-9/16 in.
kPa
PRESSURE
(57 mm) (65 mm)
2-1/32 in.
(52 mm)
1-1/4 in.
(32 mm)
2-1/16 in. (53 mm)
Mounting hole dia.
1/8-27
NPTM
0 20 40 60
100
0
300
80
600
MURPHY S WICHGAGE.
P.S.I.
Mounting
Clamp
Contact
Adjustment
1/16 in. hex
A25 Series Models
2-29/32 in. 1-51/64 in.
(46 mm)
1/8-27
NPTM 2-5/8 in.
(67 mm)
Contact
1-27/64 in.
Adjustment
(36 mm)
1/16 in. hex
Mounting
Clamp
(74 mm)
2-11/16 in. (68 mm)
Mounting hole dia.
kPa
PRESSURE
0 20 40 60
100
0
300
80
600
MURPHY S WICHGAGE.
PSI
Pressure Ranges and Factory Settings
NOTES
1. Values in ( ) are mathematical conversions from psi to kPa/MPa–they do not reflect actual second scale range. U.S.A. standard scale is psi/kPa;
U.K. standard scale is psi/bar-exact set-point shown. Consult factory for other scales.
2. For models A20PE and A25PE; the switch trip point cannot be set at either the low or high extreme of the scale. The trip point must allow for the reset differential.
3. For adjustable switch models, the trip point is adjustable only over the lower half of the scale.
Ranges Available Maximum Standard Settings High Settings* A20PABS and A25PABS Settings
Low Alarm.
psi (kPa) [bar] Pressure psi (kPa) [bar] psi (kPa) [bar] psi (kPa) [bar] psi (kPa) [bar]
0-15 (103) [1.0] 30 psi (207) 3 (21) [0.2] 12 (83) [0.8] 3 (21) [0.2] 6 (41) [0.3]
0-30 (207) [2.0] 60 psi (413) 7 (48) [0.4] 24 (165) [1.6] 7 (48) [0.4] 10 (69) [0.6]
0-50 (345) [3.5] 100 psi (690) 10 (69) [0.8] 40 (276) [2.8] 10 (69) [0.8] 13 (90) [1.0]
0-75 (517) [5.0] 150 psi (1.0MPa) 15 (103) [1.0] 60 (414) [4.0] 15 (103) [1.0] 18 (124) [1.5]
0-100 (690) [7.0] 200 psi (1.4MPa) 20 (138) [1.5] 80 (552) [5.5] 20 (138) [1.0] 23 (159) [1.5]
0-150 (1.0 MPa) [10] 300 psi (2.1 MPa) 30 (207) [2.0] 120 (827) [8.0] 30 (207) [1.5] 33 (228) [2.0]
0-200 (1.4 MPa) [14] 400 psi (2.8 MPa) 50 (345) [3.0] 150 (1 MPa) [10] 50 (345) [3.0] 53 (365) [4.0]
0-300 (2.1 MPa) [20] 500 psi (3.4 MPa) 75 (517) [5.0] 225 (1.6MPa) [15] 75 (517) [5.0] 78 (538) [5.0]
0-400 (2.8 MPa) [28] 500 psi (3.4 MPa) 150 (1.0 MPa) [7.0] 300 (2.1MPa) [20] 75 (517) [5.0] 150 (1MPa) [10]
**Low settings for Hi/Lo option same as standard settings. Hi/Lo option available for A20P and A25P models only.
.SPDT Snap-switch is the alarm switch.
Features
A. Process Connection and Port: Machined from brass bar stock. Together with
the diaphragm forms the diaphragm chamber. Typical For All Series (A25P Series Shown)
B. Diaphragm (not shown): Beryllium copper die formed and heat treated to very
close physical and metallurgical specifications.
C. Pulsation Dampener: Designed to minimize undesirable pointer chatter. It is
removable for cleaning. G
D. Dial: White letters on a black background, dual scale; others available on
request–see How to Order.
E. Case: Polycarbonate/glass filled, corrosion resistant; mounting clamp included.
F. Bezel: Polished stainless steel standard, black bezel also available.
G. Lens: Made of high-impact resistant treated polycarbonate. H
H. Pointer: Tempered nickel silver for continuity and corrosion resistance—
mounted on a machined brass post. Red tip.
I. Limit Contact: SPST contact; N.C. when low limit is met. N.O. when pointer
operates above limit. I
J. Limit Contact Adjustment: by 1/16 in. hex type wrench thru 100% of the
scale. Easy adjustment knob available.
K. Electrical Connections: Number 4 screw terminals for A20 Series; and num-C
ber 6 screw terminals for A25 Series models.
AP-94030B page 2 of 4
kPa
PRESSURE
0
10020 40 60
0
300
80
600
PSIMURPHY SWICHGAGE.
Back View
H P L
NC C NO
A
B
D
F
J
K
K
E
AP-94030B page 3 of 4
Pre-Alarm Using A20/A25PABS
Typical Internal Wiring Diagrams
The A20PABS and A25PABS features a standard limit contact for equipment
shutdown on low pressure. It also has an internal SPDT snap-switch to signal an
alarm before shutting down. When the snap-switch trips (preset point), on falling
pressure, the switch completes a circuit to activate an alarm. If the pressure continues
to fall, the face-adjustable pointer contact will make and the shutdown circuit
will be completed (see the typical diagram below for reference). The front
contact shutdown limit setting (which is adjustable) and the snap-switch are preset
at the factory. Refer to “Pressure Ranges and Factory Settings” table on opposite
page for settings. For alternative alarm before shutdown, see Magnetic
Switch model 760A or 761APH.
+ _
Battery
A20PABS
Swichgage.
Alarm Before
Shutdown
MINI-SIREN.
Opens circuit to
shutdown engine.
Shutdown Device
or Ignition Circuit
518PH
HIGH
N. C. C N. O.
ABS
G NC
R
SW1 SW2 B
Magnetic Switch
G NC
R
SW1 SW2 B
+ _
Battery
A20P Pressure
Swichgage.
A20T Temperature
Swichgage.
518PH
Energized To Run Devices
N.C. switches option
N.O. Swichgage.
C instruments
LOW
N. C. C
HIGH
N. O.
C S B
+ _
Battery
117 Magnetic Switch
Energized To Run Devices
A20P Pressure
Swichgage.
C
LOW
N. C.
INDUCTIVE AND HIGH CURRENT LOADS REQUIRE THE USE OF A
MAGNETIC SWITCH. The Swichgage contacts are for light-duty electrical
switching to operate alarms or control devices. Murphy manufactures the
Magnetic Switch for protection of the pilot-duty Swichgage limit contacts.
Tattletale. Magnetic Switches show the cause of shutdown for applications that
include: capacitor discharge or magneto ignitions, battery systems and electric
motor driven equipment. Typical wiring diagrams are shown below.
C
LOW
N. C. N. O. C
HIGH
N. C. N. O.
LOW LOW
N. C. C N. O.
ABS
L P H
N. C. C N. O.
L P H
N. C. C N. O.
L P H
N. C. C N. O.
SET RESET
LOW HIGH
HIGH
SET RESET SET RESET SET RESET
LOW LOW
LOW
N. C. C N. O.
L P H
N. C. C N. O.
L P H
N. C. C N. O.
A20P A20P-HL A20PABS A20PE
A25P A25P-HL A25PABS A25PABS-HL A25PE
Pointer shown in the shelf position. Pointer type contact rating: pilot-duty 2 A @ 30 VAC/VDC resistive.
Snap-acting switch rating: 3 A @ 30 VDC inductive. 4 A @ 125 VAC inductive.
How to Order
To order, use the diagram below. List options in ascending alphabetical order (A-Z). Example: A20P-K-100.
____ – ____ – ____
Base Model
A20P
A20PE
A20PABS
A20PG
A25P
A25PE
A25PABS
A25PG
Options.
B1 = Black bezel
EX = Explosion-proof (CSA Listed for
Class I, Div. 1, Groups C & D)*
EL = Explosion-proof less case
HL = High and low contacts
K = Knob adjusting face contact
OS = Oil sealed (Silicone Oil)
. Options not available on all models or configurations.
*A25PE-EX only is CSA listed for hazardous locations.
Range..
Dual scale (psi/kPa)
psi kPa/MPa
15 = 0-15 0-103
30 = 0-30 0-207
50 = 0-50 0-345
75 = 0-75 0-517
100 = 0-100 0-689
150 = 0-150 0-1.03
200 = 0-200 0-1.38
300 = 0-300 0-2.07
400 = 0-400 0-2.76
Single scale (bar)
1B = 0-1 bar
2B = 0-2 bar
3.5B = 0-3.5 bar
5B = 0-5 bar
7B = 0-7 bar
10B = 0-10 bar
14B = 0-14 bar
20B = 0-20 bar
28B = 0-28 bar
..Consult factory for availability of dials other than psi/kPa. Select scale
so your normal operating pressure is in the middle half of the scale.
Illumination – Order Separately A20 Series: Clamp Lite Assembly; 12 V= 05702176; 24 V= 05702177 A25 Series: N/A.
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