When standard pressure gauges reach their limits, the process industry can use diaphragm pressure gauges to measure low pressures and protect against overload in all types of applications, including ones with aggressive or hygienic media.
This article is a continuation of last week’s article, What Is a Diaphragm Pressure Gauge, and How Does It Work?
Thanks to using a flexible yet durable membrane as the sensing element, a diaphragm pressure gauge offers process industries three main advantages over other types of pressure gauges.
Reason #1 for using a diaphragm pressure gauge: measuring low pressure
Since the slightest pressure causes a diaphragm to deflect, a diaphragm pressure gauge can measure as low as 6″WC (16 mbar). Compare that to a Bourdon tube gauge, which can detect pressures only as low as 10 psi (0.6 bar).
While a capsule pressure gauge is also designed to measure very low pressure, it is suitable for dry gaseous media only. A diaphragm gauge, on the other hand, can also measure liquid and viscous media.
#2 for using a diaphragm pressure gauge: overload protection
Pressure overload, also referred to as overpressure, is one of the common reasons for gauge failure. However, a diaphragm pressure gauge can withstand significantly higher maximum pressures than standard pressure gauges.
WIKA’s diaphragm pressure gauges for process industries have an overload safety of up to five times the full-scale value, with the upper limit at 600 psi for model 43X.50/43X.30 (safety version), whereas it is only 1.3 times that in a standard Bourdon tube gauge. The source of the overload safety is the upper housing, which provides a solid surface for the diaphragm to push against. The extent of the overload limit depends on the range. For example, at a range of 0…100″WC, the maximum overload limit is 500″WC – five times the full-scale range.
For overload protection greater than five times the full-scale value, WIKA offers a special version of models 43X.56/43X.36 (safety version). The overload safety can be increased up to 6000 psi (400 bar), independent of the pressure range, by selecting the high overload safe version model 43X.36, which comes in a solid front safety design. Model 43X.50 is available for maximum overpressure up to 3600 psi (250 bar), independent of the pressure range.
This high overload safety comes from the following design features:
- The truncated waves of the corrugated diaphragm (1) gives it a larger contact area, thus spreading out the pressure.
- The surface area of the upper flange (2) matches the same contour as the diaphragm preventing any deformation under extreme high pressure. (For vacuum protection at very low pressure ranges, the same principle is applied to the bottom housing by machining the surface area in the same contour as the diaphragm.)
- The support materials (bolts, flanges) are strong enough to withstand such high pressures.
Reason #3 for using a diaphragm pressure gauge: aggressive and sensitive media
Certain process media can damage a gauge’s inner mechanism, while others can clog the pressure port. To measure the pressure of liquids and gases that are corrosive, hot, viscous, crystallizing, or contaminated, the process industry can use a diaphragm pressure gauge.
Measuring solution for corrosive and hot media
Diaphragms can be made with a variety of special materials that help them withstand aggressive liquids and gases, such as those found in fertilizer production. Coating options for the process facing side of the diaphragms include tantalum, titanium, gold, platinum, Hastelloy, PTFE, and other highly resistant polymers. In some cases, the entire diaphragm is made of the exotic metal or alloy. These special materials are not only extremely resistant, but also meet the elasticity and sealing requirements of the measuring task. For applications with extremely corrosive media, the lower flange of the diaphragm pressure gauge can also be lined with special materials, thereby protecting all the wetted parts. Diaphragm gauges with special materials are essential in the chemical, petrochemical, and oil and gas industries.
Note: Lower flanges with threaded connections (1/2″ NPT or 3/4″ NPT male or female) cannot be lined with special materials. Only so-called “open flange” connections, such as 1″ 150# per ASME B16.5, can be lined with special material.
Measuring solution for viscous, crystallizing, and contaminated media
Several process industries, such as water/wastewater treatment, often work with liquids that are viscous, crystallizing, or contaminated. Such media can clog the narrow pressure ports in a threaded male connection. A diaphragm pressure gauge with a 1/2″ NPT female connection or open flange connections, such as 1″ 150#, eliminates such issues. With a nominal width of 1″ or 2″, this type of pressure connection has a large pressure chamber in which large particulates and sticky liquids do not remain. In addition, the lower flanges can be equipped with 1/4″ NPT female flushing connections in order to clean the pressure chamber.
Measuring solution for sanitary processes
The food & beverage and pharmaceutical/biotechnology industries work with media that follow strict sanitary protocols. To eliminate a gauge’s dead spaces, which are prime environments for bacteria and fungi to grow, use a diaphragm pressure gauge with a flush diaphragm. In this design, the pressure element is welded directly to the hygienic process connection.
WIKA also offers two solutions for sanitary processes that cannot risk contamination in the event of a system fluid leak.
- A dry cell sanitary gauge like the PG43SA-S has a purely mechanical (rather than hydraulic) pressure transmission system.
- Our patented diaphragm monitoring system has two diaphragm seals. In the event that the outer one is breached, the device gives a warning. Meanwhile, the inner diaphragm takes over until the primary DS can be replaced.
WIKA USA, Your Partner for Industrial Pressure Gauges
WIKA offers a complete portfolio of pressure solutions for a variety of industries. With so many choices, we understand that it can be difficult to select the right pressure gauge for your particular application. That’s why we encourage you to contact our specialists, who are happy to offer personalized advice and work with you to find the ideal pressure instruments.
Products mentioned in this blog:
• 432.30/433.30 Sealgauge Diaphragm Pressure Gauge, Process Industry Series, Solid Front Case
• 452.50/453.50 Sealgauge Diaphragm Pressure Gauge, Process Industry Series
• 432.56/432.36 Sealgauge Diaphragm Pressure Gauge, Process Industry Series
• 432.36/433.36 Sealgauge Diaphragm Pressure Gauge, Process Industry Series
• PG43SA-S Diaphragm Pressure Gauge for sanitary applications (dry cell sanitary gauge with flush diaphragm)