Magnehelic® Differential Pressure Gauges

Product Overview

Dwyer® Magnehelic® gauges are designed for high accuracy, guaranteed within 2% of full scale. They offer a wide choice of 81 models to suit precise needs. Utilizing Dwyer's simple, frictionless Magnehelic® gage movement, these gauges quickly indicate low air or non-corrosive gas pressures, whether positive, negative (vacuum), or differential. The design is resistant to shock, vibration, and over-pressures, eliminating the need for manometer fluid that can evaporate, freeze, or cause leveling problems. These gauges are also cost-effective.

The Magnehelic® gauge is the industry standard for measuring fan and blower pressures, filter resistance, air velocity, furnace draft, pressure drop across orifice plates, liquid levels with bubbler systems, and pressures in fluid amplifier or fluidic systems. They are also used to check gas-air ratio controls and automatic valves, and to monitor blood and respiratory pressures in medical care equipment.

Note: May be used with Hydrogen. When ordering a Buna-N diaphragm, pressures must be less than 35 psi.

Mounting

A single case size is used for most Magnehelic® gage models. They can be flush or surface mounted using standard hardware. An optional A-610 Pipe Mounting Kit allows convenient installation on horizontal or vertical 1-1/4" to 2" pipes. While calibrated for vertical position, many ranges above 1" can be used at any angle by simply re-zeroing. For maximum accuracy, however, they must be calibrated in the same position in which they are used. These characteristics make Magnehelic® gages ideal for both stationary and portable applications. Flush panel mounting requires a 4-9/16" hole. Complete mounting and connection fittings, along with instructions, are provided with each instrument.

Vent Valves: For applications where pressure is continuous and the Magnehelic® gage is connected by metal or plastic tubing that cannot be easily removed, Dwyer suggests using A-310A vent valves. These allow pressure to be removed to check or re-zero the gage.

High and Medium Pressure Models: Installation is similar to standard gages, but requires a 4-13/16" hole for flush mounting. Medium pressure construction is rated for internal pressures up to 35 psig, and high pressure up to 80 psig. These options are available for all models. Due to their larger cases, medium and high pressure models do not fit in portable cases. Installing the A-321 safety relief valve on standard Magnehelic® gages provides adequate protection against infrequent overpressure.

Specifications

• Service: Air and non-combustible, compatible gases. (Natural Gas option available.)
• Wetted Materials: Consult factory.
• Housing: Die cast aluminum case and bezel with acrylic cover. Exterior finish is coated gray to withstand 168-hour salt spray corrosion test.
• Accuracy: ±2% of full scale (±3% on -0, -100 Pa, -125 Pa, -10MM, and ±4% on -00, -60 Pa, -6MM ranges) throughout range at 70°F (21.1°C).
• Pressure Limits: -20" Hg to 15 psig (-0.677 bar to 1.034 bar). MP option: 35 psig (2.41 bar). HP option: 80 psig (5.52 bar).
• Overpressure: Relief plug opens at approximately 25 psig (1.72 bar) on standard gages only.
• Temperature Limits: 20°F to 140°F (-6.67°C to 60°C). (*Low temperature models available as special option.)
• Size: 4" (101.6 mm) Diameter dial face.
• Mounting Orientation: Diaphragm in vertical position. Consult factory for other position orientations.
• Process Connections: 1/8" female NPT duplicate high and low pressure taps (one pair side, one pair back).
• Weight: 1 lb 2 oz (510 g). MP & HP: 2 lb 2 oz (963 g).
• Standard Accessories: Two 1/8" NPT plugs for duplicate pressure taps, two 1/8" pipe thread to rubber tubing adapters, and three flush mounting adapters with screws. (Mounting and snap ring retainer substituted for 3 adapters in MP & HP gage accessories.)
• Note: For applications with high cycle rates within the gage's total pressure rating, a next higher rating is recommended. See Medium and High pressure options.

Options and Accessories

• Transparent Overlays: Available in red and green to highlight and emphasize critical pressures.
• Adjustable Signal Flag: Integral with plastic gage cover. Available for most models except those with medium or high pressure construction. Can be ordered with the gage or separately.
• LED Setpoint Indicator: A bright red LED on the right of the scale indicates when a setpoint is reached. The unit operates on 12-24 VDC and requires an MP or HP style cover and bezel.
• A-432 Portable Kit: Includes a carrying case with any Magnehelic® gage of standard range (except high pressure connection), 9 ft (2.7 m) of 3/16" I.D. rubber tubing, a stand/hang bracket, and a terminal tube with holder.
• A-605 Air Filter Gage Accessory Kit: Adapts any standard Magnehelic® gage for use as an air filter gage. Includes an aluminum surface mounting bracket with screws, two 5 ft (1.5m) lengths of 1/4" aluminum tubing, two static pressure tips with integral compression fittings, and two molded plastic vent valves with integral compression fittings.

Quality Design and Construction Features

The Magnehelic® gauge features a bezel that provides a flange for flush mounting in a panel. The clear plastic face is highly resistant to breakage and offers undistorted viewing of the pointer and scale. The red-tipped pointer, made of heat-treated aluminum tubing, is easy to see and rigidly mounted on the helix shaft. Pointer stops made of molded rubber prevent pointer over-travel without damage. A "Wishbone" assembly mounts the helix, its jeweled bearings, and the pointer shaft. Jeweled bearings are shock-resistant mounted for virtually friction-free motion of the helix, which is damped with high-viscosity silicone fluid. The zero adjustment screw is conveniently located in the plastic cover, accessible without removing the cover. An O-ring seal ensures pressure tightness of the case. A blowout plug of silicone rubber protects against overpressure on 15 psig rated models, opening at approximately 25 psig. The die-cast aluminum case is precision-made and iridite-dipped to withstand 168-hour salt spray corrosion tests. The exterior is finished in baked dark gray hammerloid. A single case size is used for all standard pressure options and for both surface and flush mounting. A silicone rubber diaphragm with an integrally molded O-ring is supported by front and rear plates, locked and sealed in position with a sealing plate and retaining ring. Diaphragm motion is restricted to prevent damage from overpressures. The calibrated range spring is made of flat spring steel; its small amplitude of motion ensures consistency and long life, reacting to diaphragm pressure. The live length is adjustable for calibration. A Samarium Cobalt magnet, mounted at one end of the range spring, rotates the helix without mechanical linkages.

Series 2000 Magnehelic® Gage - Models and Ranges

For special scales furnished in ounces per square inch, inches of mercury, metric units, square root scales for volumetric flow, etc., contact the factory. Page V shows examples of special models built for OEM customers.

Accessories

• A-299: Surface Mounting Bracket
• A-300: Flat Flush Mounting Bracket
• A-310A: 3-Way Vent Valve
• A-321: Safety Relief Valve
• A-432: Portable Kit
• A-448: 3-piece magnet kit for mounting Magnehelic® gage directly to magnetic surface
• A-605: Air Filter Kit
• A-610: Pipe Mount Kit

Options

• ASF: Adjustable Signal Flag
• HP: High Pressure Option
• LT: Low Temperatures to -20°F
• MP: Med. Pressure Option
• SP: Setpoint Indicator
• Scale Overlays: Red, Green, Mirrored or Combination, Specify Locations

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