For Magnehelic®, Capsuhelic® and Minihelic® Gages
These applications serve only to suggest the wide range of applications served by the versatile Magnehelic®, Capsuhelic® and Minihelic® series of low pressure gages. Although many of the applications obviously solve problems for users of air conditioning, heating and ventilating equipment, a number of others involve monitoring low pressures in pollution control devices, clean rooms, fluidic systems, medical-surgical patient care equipment and similar uses.
As a gage to check air filters
Gage gives an instant visual indication when filters need servicing. Select a model with range appropriate to the filter manufacturer's recommendation for maximum permissible pressure drop across filter. Install a gage with red pointer flag (an option), to be set at the maximum allowable pressure drop point for air volume being handled. This assures easy reading of the gage, even by relatively inexperienced operators.
To sense static pressure
For the most accurate measurement of static pressure in an air stream, use gage connected to a static pressure tip such as Dwyer Model A-301. The next most accurate pick-up is a smooth, burr-free solder connection flush with the inside surface of the duct. Only slightly less accurate is a simple connection such as the Dwyer Model A-307.
To measure air velocity
Connect a Magnehelic® or Minihelic® gage to pitot tube in the air stream. Or, the simple alternative method pictured above shows a static tap plus a simple tube in center of duct to pick up total pressure. The differential pressure reading on gage is center velocity pressure which may be converted to air velocity.
To determine flow
In this set-up, gage measures the pressure drop across a sharp-edged orifice plate. Details regarding available sizes, ranges, installation, and limitations are available from orifice plate manufacturers and from standard handbooks.
As an orifice meter
Magnehelic® or Minihelic® gages can be used as orifice meters by purging the orifice with air pressure to protect gage from direct contact with fluid or to prevent clogged meter lines. Gage is shown connected to two Dwyer flowmeters with constant differential pressure regulators - one for the low pressure tap line and one for the high pressure side. (Capsuhelic® gage may be used without purge on compatible liquid streams.)
Air volume measurement
An elliptical flow nozzle with an egg crate air straightener located upstream provides an accurate, easily constructed air volume measurement system. Air velocity distribution at the point of discharge across the outlet of the nozzle is uniform; static pressure is zero. Consequently, the total pressure upstream from the nozzle is the velocity pressure at the nozzle outlet - and the volume of low is easily calculated.
To monitor engine or compressor air filters
Gage gives continual reading of air pressure drop across filter and signals need for cleaning or replacement of filter. Gage is installed with negative or low pressure port connected to intake pipe between filter and engine or compressor. A Capsuhelic® gage can be used to monitor pressure drop across the oil filter.
For Photohelic® and Capsu-Photohelic® Gages
Dwyer Photohelic® and Capsu-Photohelic® switch/gages furnish all the advantages of the Magnehelic® gage plus one or two easily set pressure switches with visible set point indicators. The switches provide an electrical signal to operate audio or visual alarms or control motors, fans, valves and other equipment with reliable accuracy.
To measure liquid level
Use a Photohelic®, Magnehelic®, or Minihelic® gage in conjunction with a Dwyer flowmeter with constant differential pressure regulator as show. Flowmeter provides constant rate of purge air to dip tube. Changes in liquid level affect head, causing static pressure changes inside tube. These changes are sensed by the gage. This same kind of setup will also detect specific gravity changes in the liquid if level is kept constant. Using a Dwyer Photohelic® pressure switch/gage instead of the Magnehelic® permits both measuring and controlling liquid level plus easily changing the level control settings.
To control pressure in air-inflated buildings
Photohelic® switch/gage senses over-pressure that may extend building, or loss of pressure that may cause collapse, and controls the blower to maintain correct pressure. Gage is easily reset to conserve power - or provide extra pressure to resist strong winds.
To control material weight
On paper making or textile machinery, a Photohelic® switch/gage controls weight of material gathered by sensing pressure changes caused by changes in permeability and thickness of the material.
For life support or kidney machines
Photohelic® switch/gage controls pressure on circulating system of machine and alarms in event of too high or low pressure.
Monitor air conditioning systems
Adjustments in air flow due to seasonal changes may require resetting the control points on a regular basis. The Photohelic® unit's ability to monitor pressures through the gage portion also permits accumulation of operating data. This is useful in adjusting operation of variable pressure and volume systems and in making system changes when necessary.