The Dwyer Magnehelic® 2000 Series is a differential pressure gage designed for measuring the difference in pressure between two points. It utilizes a flexible diaphragm and magnetic linkage to provide a dial-type reading. These gages are suitable for applications involving air and non-combustible, compatible gases, and are commonly used in air filtration monitoring, HVAC systems, and various industrial processes. Standard accessories include necessary adapters and mounting hardware. The device is characterized by its ease of reading, low cost, and ability to withstand vibration.
Operating Principles
The Magnehelic® gage operates based on the principle of differential pressure. The device consists of two pressure-tight compartments separated by a flexible diaphragm. The space inside the gage case constitutes the “high” pressure side, while a sealed chamber behind the diaphragm serves as the “low” pressure side. Pressure differences between these two sides cause the diaphragm to deflect. This deflection is linked to a leaf spring, which in turn moves a pointer via a magnetic linkage. The position of the pointer indicates the differential pressure. The gages are calibrated with the diaphragm in a vertical position for maximum accuracy, though some models can function in other orientations with re-zeroing.
Specifications
The following specifications are derived from the provided documentation:
- Service: Air and non-combustible, compatible gases. A Natural Gas option is available.
- Wetted Materials: Details are available by consulting the factory.
- Housing: Die cast aluminum case and bezel with an acrylic cover. The MP model utilizes a polycarbonate cover.
- Dimensions: 4-3/4 inches in diameter and 2-3/16 inches deep.
- Weight: 1 lb 2 oz (standard models); 2 lb 2 oz (MP & HP models).
- Accuracy: Plus or minus 2% of full scale (Model 2000-0, 3%; 2000-00, 4%).
- Pressure Rating: 15 PSI (0.35 bar).
- Ambient Temperature Range: 20° to 140°F (-7 to 60°C).
- Process Connections: 1/8˝ female NPT duplicate high and low pressure taps.
- Agency Approvals: RoHS compliant.
Installation Procedures
Several mounting options are available for the Magnehelic® gage:
- Surface Mounting: Mounting holes are located 120° apart on a 4-1/8” diameter circle. Use No. 6-32 machine screws of appropriate length.
- Flush Mounting: A 4-9/16” diameter opening is required in the panel for standard models, and a 4-3/4” diameter opening for MP and HP models. Secure the gage with No. 6-32 machine screws and adapters.
- Pipe Mounting: An optional A-610 pipe mounting kit is available for mounting on 1-1/4” - 2” pipe.
When installing, it is recommended to select a location free from excessive vibration and direct sunlight. Sensing lines can be run any necessary distance, though longer lengths may slightly increase response time. Lines should not be restricted. If pointer oscillation occurs due to pulsating pressures or vibration, contacting the factory for damping solutions is advised.
Zeroing and Adjustment
After installation, the gage should be zeroed. This is accomplished by setting the indicating pointer exactly on the zero mark using the external zero adjust screw located on the bottom of the cover. It is crucial to ensure both high and low pressure taps are open to the atmosphere during this adjustment. Occasional zero setting is the only field adjustment typically required.
Standard Accessories
The Magnehelic® gage is supplied with the following standard accessories:
- Two 1/8˝ NPT plugs for duplicate pressure taps.
- Two 1/8˝ pipe thread to rubber tubing adapters.
- Three flush mounting adapters with screws (mounting and snap ring retainer substituted for 3 adapters in MP & HP gage accessories).
- Air Filter accessories include a mounting panel with screws, two static pressure tips with integral compression fittings, two five-foot lengths of 1/4˝ aluminum tubing, and two molded plastic vent valves with compression fittings.
MP and HP gage accessories include a mounting ring and snap ring retainer substituted for the three adapters, and 1/4” compression fittings replace the 1/8” pipe thread to rubber tubing adapters.
Overpressure Protection
Standard Magnehelic® gages are rated for a maximum pressure of 15 psig. They incorporate a rubber plug on the rear that functions as a relief valve, unseating and venting the gage interior when overpressure reaches approximately 25 psig (excluding MP and HP models). Four spacer pads maintain a .023˝ clearance when surface mounted, providing a path for pressure relief. These pads should not be obstructed.
Important Cautions
The documentation includes the following cautions:
- The gage is intended for use with air or compatible gases only.
- For applications with high cycle rates within the gage’s total pressure rating, a higher-rated model is recommended.
- The gage should not be used with hydrogen gas unless ordered with a Buna-N diaphragm, and pressure must be less than 35 psi.
- For repeated over-ranging or high cycle rates, contacting the factory is advised.
Model-Specific Considerations
The documentation highlights some differences between standard models and MP/HP models:
- MP and HP models require a 4-3/4” diameter panel cutout for flush mounting, compared to 4-9/16” for standard models.
- MP and HP accessories differ in the adapters and fittings provided.
- Overpressure protection mechanisms differ between standard and MP/HP models.
Maintenance
The Magnehelic® gage requires minimal maintenance. The documentation states that no maintenance is typically required in the field, beyond occasional zero setting.
Conclusion
The Dwyer Magnehelic® 2000 Series differential pressure gage provides a reliable and cost-effective solution for measuring pressure differences in various applications. Proper installation, zeroing, and adherence to the specified cautions are essential for accurate and safe operation. The availability of different mounting options and accessories allows for flexibility in adapting the gage to specific needs. The device’s robust design and minimal maintenance requirements contribute to its long-term usability.