Differential-pressure gauges are widely known as the largest “specialty type” pressure gauge category. They are used in filtration, level flow.Differential pressure gauges can greatly reduce operator error, increase process efficiency, protect costly equipment, reduce training, and reduce maintenance time.
A differential pressure gauge is a visual indicator,manufactured to analyze and illustrate the difference between two pressure points within a process system. The gauge usually has dual inlet valves that are each connected to the pressure points being monitored. A differential pressure gauge reduces the process by finding the non-similarities between the points. Without this differential pressure gauge, a controller or control system would require to watch two separate gauges and conclude the difference in readings.
How Differential Pressure Gauges Work
Unlike standard pressure gauges, which measure pressure at a single point in a system, DP gauges measure the pressure at two points and display the pressure difference between those two points on a single dial. The pressure measured could be 115 PSI before a filter and 100 PSI after the filter, allowing the DP gauge to read the difference, which is 15 PSI, referred to as15 PSI differential. That represents a 15 PSI pressure drop caused by the filter.
Like filters, other elements in a process system may degrade over time and may need to be monitored. Heat exchangers, pumps, valves, condensers and evaporators all create pressure drop when they become worn or clogged. Like filters, the problems they cause can be severe.
Monitoring pressure drop —wherever it occurs —can offer incremental opportunities for improving process conditions and savings. Pumps and compressors move liquid or air within each process at a high cost, sometimes being driven harder than required. Reducing pressure lost within each process component may reduce the need for larger, more expensive pumps and compressors, and generally create more efficient flow and a better end product.
The most popular application for differential pressure gauges is filtration. A filter removes unwanted particles or contaminants from a gas or liquid system. When a filter becomes clogged, efficiency and pressure drops. Here are four relatively risky methods to identify this condition:
Like filters,heat exchangers often protect equipment that costs many times that amount. Over time heat exchangers develop rust or become clogged, indicating a time to flush or backwash.
Differential pressure gauges also measure liquid level. Again, like flowmeters, there are many types of level gauges. A simple, relatively inexpensive solution is to use a differential pressure gauge to indicate the level of a liquid within a tank. In open tanks, the high-pressure side of a DP gauge is ported to the bottom of a tank, while the low-pressure side is mated to the atmosphere. In this scenario the DP gauge is measuring a column of liquid within the tank, resulting in a reading that reflects the height of the liquid within the tank, often displaying inches or feet of water readings or percent-full readings.
For pressurized tanks, such as cryogenic tanks, again the DP high-pressure side is ported to the bottom of the tank, but the low-pressure side is ported to the top of the tank. The result is a measurement of the column of liquid in the tank (the liquid height), often giving a read-out in inches of water or percent full.
The Benefit of Differential-Pressure Measurement
What’s common amongst these applications is the simplicity. In all the instances there is only the need to tap into a pipe or tank. For flow, there is no need for a large, heavy, expensive flowmeter; or in the case a liquid level, 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 the present 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.
Capital equipment and processes are expensive. They can be protected by a low-cost differential pressure gauge.