05704255 – Murphy Differential Pressure Swichgage – Model A20P-100


A20P-100 2″ Pressure Swichgage® (05704255)

The A20P-100 Pressure Swichgage® is a 2″ dial, diaphragm-actuated pressure-indicating gage with a built-in electrical limit switch, which is used for tripping alarms and/or shutdown devices. This dual-scale instrument has a range of 0-100 psi (690 kPa) [7.0 bar]. The gage mechanism is enclosed in a polycarbonate, break-resistant case and lens. A polished stainless-steel bezel and O-ring seals help protect this rugged instrument from the external environment. Accuracy and protection from moderate overpressure are assured by a unique, unitized diaphragm chamber. A built-in pulsation dampener helps eliminate pointer flutter and is removable for cleaning. Inside the A20P-100, the tempered nickel silver 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 a self-cleaning motion to ensure electrical continuity. The A20P-100 Pressure Swichgage® was specifically designed to protect engines and equipment in oil field, marine, irrigation, construction and trucking
applications by monitoring engine lube pressure, water pump pressure, hydraulic pressure and air pressure. This popular instrument features a beryllium copper diaphragm sensing element and a 1/8-27 NPTM brass process connection. The adjustable limit contact is an SPDT contact; pilot-duty only, 2A @ 30 VAC/DC; closed when the low limit is met, and open when the pointer is in normal operating range.

Estimate available in 28 working days from Italy to Italy.

This product may vary on delivery times, as factories do not guarantee production due to lack of raw materials.

Availability: Available on backorder SKU: 05704255 Categories: , Tags: ,


Product Specifications:

  • Dial: White on black, dual scale (U.S.A. standard scale is psi/kPa; U.K. standard scale is psi/bar)
  • Case: Polycarbonate / Glass filled, corrosion-resistant; steel mounting clamp included
  • Bezel: Polished stainless steel, standard; others are available
  • Lens: Polycarbonate, high impact
  • Temperature Range:
    • Ambient: -40° to 150° F (-40° to 66° C)
    • Process: -40° to 250° F (-40° to 121° C)
  • Process Connection: 1/8-27 NPTM brass
  • Sensing Element: Beryllium copper diaphragm
  • Gage Accuracy: ±3% maximum across scale
  • Adjustable Limit Contact: SPST contact; pilot duty only, 2 A @ 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 1/16 in. hex wrench through 100% of scale
  • Wiring: A20P Number 4 screw terminals
  • Unit Weight: A20 Series: 0.23 kg
  • Unit Dimensions: A20 Series: 3 x 3 x 3 in. (76 x 76 x 76 mm)


a20 series models dimension

Pressure Ranges and Factory Settings:

  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;
  2. For models A20PE and A25PE; the switch trip point cannot be set at either the loe 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 AvailableMaximum PressureStandard SettingHigh Settings*A20PABS and A25PABS Setting
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(1.0Mpa)[10]300 psi (2.1MPa)30(207)[2.0]120(827)[8.0]30(207)[1.5]33(228)[2.0]
0-200(1.4Mpa)[14]400 psi (2.8MPa)50(345)[3.0]150(1Mpa)[1.0]50(345)[3.0]53(365)[4.0]
0-300(2.1Mpa)[20]500 psi (3.4MPa)75(517)[5.0]225(1.6Mpa)[1.5]75(517)[5.0]78(538)[5.0]
0-400(2.8Mpa)[28]500 psi (3.4MPa)150(1.0Mpa)[7.0]300(2.1Mpa)[20]75(517)[5.0]150(1Mpa)[10]

*Low Setting for Hi/Lo option same as standard setting. Hi/Lo option avaible for A20P and A25P models only.**SPDT Snap-switch is the alarm switch.
**SPDT Snap-switch is the alarm switch.

Magnetic Switch

Inductive and high current loads require the use of a magnetic switch. The Swichgage contacts are for the 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 show below.

magnetic switch a20p

Pre-Alarm Using A20/A25PABS

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 (wich is adjustable) and the snap-switch are preset at the factory. Refer to “Pressure Ranges and Factory Settings” table on opposite page for setting. For alternative alarm before shutdown, see Magnetic Switch model 760A or 761APH.

pre alarm using a20-25pabs

Typical Internal Wiring Diagrams

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:

Base Model: A20PG
100: 0-100 PSI; 0-689 kPa/MPa
Part Number: 05704255

Additional information

Weight0,23 kg


05704255, A20P-100