Diaphragm Gauges ASME Grade A-1% Accuracy

Brand: Marsh Bellofram Group of Companies

Marsh low-pressure diaphragm gauges are universally known for their dependable performance and accuracy, with ASME Grade A-1% accuracy for ranges above 30″ of water.

Available ranges include vacuum and pressure in inches of water, ounces per square inch and millimeters of mercury.

The units incorporate a unique bronze diaphragm element and solid safecase design, allowing for accurate low-pressure readings in support of a variety of applications.

How Marsh Diaphragm Gauges Work
Diaphragm gauges are sensitive instruments used in low-pressure applications typically not exceeding 10 psi. The diaphragm capsule is an elastic metal sensing element comprised of two thin wall diaphragms whose sides are soldered together to make the capsule.

Whenever air or gas enters the intake port (gauge connection), it travels into the diaphragm capsule. As vacuum or pressure is applied to the diaphragm capsule, the walls of the capsule expand and contract in response to the change in pressure. This change is then transferred to a rotation rod and arm that rest on the outside of the capsule.

The rotation rod is connected to a geared movement through a linkage system. Connected to a shaft, this system then drives the pointer over a dial marked in appropriate pressure or vacuum units for repeatable, high-precision accuracy.
  • Dial Sizes: 2-1/2", 3-1/2", 4-1/2"
  • Four Case Styles 
  • Accuracy: ASME B40.1 - 2/1/2%



  • For Ranges 30” H₂O & above: ASME Grade A = ± 2/1/2 % (± 1 % of Range across middle half of scale)
  • For Ranges below 30” H₂O: ± 3/1/3 % (± 1 % of Range across middle half of scale)

Case Sizes

  • 4-1/2”
  • 3-1/2”
  • 2-1/2”

Case Material

  • Steel, Black Painted

Case Style

  • UC - U-Clamp Mount
  • LM - Lower Mount
  • FF - Three-holed Front Flanged Mount
  • CB - Center Back Mount

Diaphragm & Socket

  • Phosphor Bronze Diaphragm


  • Brass Sector and Pinion


  • 1/4” NPT
  • 1⁄8” NPT

Dial Standard

  • Triple Scale: oz./in², in H₂O, & kPa
  • Dual Scale with kPa

Dial Color

  • Black Markings on White


  • Aluminum, Black Painted


  • 4-1⁄2”: flat acrylic with Steel Friction Ring
  • 2-1/2” & 3-1/2”: Acrylic Twist-in Clearlok


  • 0.013” Standard. No restrictor on 0 to 10” H₂O range


  • 2-1/2”: 0.5 lb
  • 3-1/2”: 0.7 lb
  • 4-1⁄2”: 1.0 lb

  • HVAC systems
  • Low pressure gas burner systems

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