Fluid Power Journal

Why Differential Pressure Gauges?

Reduce Errors, Improve Operations and Protect Equipment with DP Monitoring

By Jim Gill, Director of Sales & Marketing, Orange Research


Differential pressure gauges are widely recognized as the largest “specialty type” pressure gauge category. They are used in filtration, flow and level. For many the need for a single differential pressure gauge, switch or transmitter is not immediately understood. There are some surprising benefits to installing a differential pressure (DP) gauge.


How Differential Pressure Gauges Work



The most popular application for differential pressure gauges is filtration. This application serves as an easy-to-understand explanation for the need for a differential pressure gauge. A filter removes unwanted particles or contaminants from a gas or liquid system. When a filter becomes clogged, efficiency and pressure drop. Here are four relatively risky methods to identify this condition:

1. Scheduled Maintenance, Which Invites Waste & Contamination


In addition, many filter housings have a dozen or more bolts to unscrew to view the filter element inside. The maintenance crew often finds a relatively clean filter. Alternatively, the crew may find the filter long overdue for maintenance, the process having been starved of required fluids. Even worse, the filter may have been compromised with “filter blow-by”, a condition where the filter element is torn, creating a hole where contaminants have been allowed to pass through unfiltered, which can cause extensive damage.



3. Monitoring Filtration with Two Pressure Gauges Compounds Inaccuracies & Confusion

Mounting two similar standard pressure gauges on a filter, one on the filter inlet and one on the outlet, is a common method of determining filter condition. As the filter becomes clogged, the inlet pressure gauge begins to read higher than the outlet pressure. By the time the filter is ready to be backwashed, the difference between the two pressure gauge readings may be 15psi or more, depending on the filter type. In order to obtain this reading, the user needs to subtract the lower reading from the higher reading.


Second, and this is possibly the bigger issue, many operators have not been trained as to why there are two pressure gauges on the filter. History shows that many operators, presented with the question of why there are two pressure gauges, simply cannot answer the question. Very often the operators have no idea that they are supposed to subtract one pressure gauge reading from the other. Even if they do, they may not truly understand the importance of that calculation.



The Solution – No Math, No Mistakes & Easy to Understand


A differential pressure gauge dial can also feature a red arc indicating that the filter is clogged, or is about to become clogged–also known as the “alarm condition.” This alarm condition would be enhanced further if the DP gauge dial had the words “filter” or “clean” and “dirty” on the single DP gauge dial face. None of this is possible with two separate pressure gauges.

In addition, with one DP gauge, a switch or transmitter may be added as a standard option. This has the benefit of creating a local and remote monitor in one instrument, so others, who are not on the floor but perhaps in a command center, can see the filter condition.

In this world of Lean solutions the term “Poka-Yoke” comes to mind, which roughly means “mistake-proof”. Essentially a DP gauge can present the operator with a reading that is immediately understood. This not only reduces errors but simplifies operator training.

Once a DP gauge shows a reading “in the red,” points to dirty, or has an electrical output from the switch or transmitter, the alarm condition is understood. The operator can then take the appropriate action needed to remedy the situation. The filter can be serviced at the proper time, not too early and not too late.

More Applications for Differential Pressure Gauges



Differential Pressure in Heat Exchangers



Differential Pressure in Flow


The popular solution is to cut the pipe, install an orifice plate and measure the pressure drop across the orifice plate. A DP flow meter is designed to handle the square root relationship between the flow and the differential pressure created, using Bernoulli’s Law. This represents a high accuracy solution at a lost cost.


Differential Pressure in Liquid Level



The Benefit of Differential Pressure Measurement

What’s common among these applications is the simplicity. In all instances there is only the need to tap into a pipe or tank. For flow, there is no need for a large, heavy, expensive flow meter or in the case of a liquid level, a long float-type rod or mechanism. Differential pressure gauges can be much less invasive and therefore less costly. Because of the simplicity, maintenance on differential based systems is often relatively fast and easy.

While there are alternatives to differential pressure gauges, they can be costly when risks and operational expenses are considered. Monitoring differential pressure reduces confusion, errors, and inaccuracies, and presents conditions on a single, easy-to-read dial. In addition, switches or transmitters can be added to allow for local and remote monitoring in one unit.


About Orange Research: Headquartered in Milford, CT, USA, Orange Research, Inc. is one of North America’s premier manufacturers of differential pressure gauges, switches and transmitters. The company’s products are recognized as rugged and reliable solutions, often acting as a “install them and forget them” type of instrument. In business for over 50 years, Orange Research serves customers in a diverse range of industries including cryogenics, fluid control, hydraulics, industrial vehicles, medical, oil and gas, power generation, semiconductors, waste processing, water treatment and more. Orange Research is recognized as offering the world’s widest selection of differential pressure and flow products, and has earned a reputation as “the differential pressure people”.

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One thought on “Why Differential Pressure Gauges?

  1. Dean Phillips

    I had no idea that the most popular application for differential pressure gauges is filtration, which can be used to remove unwanted particles or contaminants from a gas or liquid system. My brother recently applied to work at a factory that specializes in turning water into electrical energy. I think it would be very beneficial for them if they used pressure gauges to ensure that none of their equipment is overworked and gets damaged. If he gets the job, he will be able to figure out if they use gauges and can recommend they purchase some if they do not.


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