There are multiple factors that influence when selecting a pressure gauge since the market offers several brands and models with different characteristics, but to make the process easier, the meaning of the word must be taken into account. S.T.A.M.P.E.D.
S.T.A.M.P.E.D. is an acronym that refers to: Size, Temperature, Application, Material/Media, Pressure, Ends, and Delivery, which will help determine which pressure gauge is appropriate for your specific situation.
There is a simple mnemonic to remember the seven determining factors in selecting the appropriate pressure gauge:
1. S – Size
Mechanical pressure gauges are available in a variety of nominal sizes, and which one you choose depends on your readability, space, and accuracy requirements. The larger the dial, the more divisions there will be to get a more accurate reading, and the easier it will be to do this from a distance – an important consideration if technicians can’t get close to the gauge. However, some applications do not have that space. For this reason, there are pressure gauges that range from 1.5″ (40 mm) to 10″ (250 mm) in diameter.
Another factor to consider is the size of the end connection, which will determine what size gauge is required. For example, a 1.5″ diameter gauge is too small to accommodate a ½” size fitting, based on the flat area of the faucet in proportion to the case profile.
2. T- Temperature
Both the ambient temperature and the temperature of the medium will determine the material of the parts in contact with the medium (stainless steel, nickel alloy, etc.) and whether you will have a dry case or be filled with liquid. The lower the ambient temperature, the more likely a liquid-filled gauge is the correct choice.
If the temperature of the medium reaches 60°C or more, a stainless steel pressure gauge should be used, since copper-zinc alloy pressure gauges are soldered, and the solder begins to break at that temperature. Stainless steel gauges can withstand temperatures up to 200°C (392°F), depending on configuration.
3. A – Application
This letter basically answers, for which industry and process is the pressure gauge needed?
Manometers for drinking water applications must be lead-free, while process industries such as refineries and pharmaceuticals require industrial process instruments. Cryogenic gas tanks require a pressure solution that measures both differential and service pressure, and for oxygen service, they are clean of oils and greases. Pressure gauges used in sanitary processes must be of hygienic design.
For greater reliability and long life in high vibration applications, a glycerin-filled gauge should be used to dampen movement and protect the internal mechanism of the instrument. It should be noted that in high pressure cycles (pulsations), glycerin must be used together with a restrictor or damper.
4. M- Medium
The medium that the pipe carries and with which the pressure gauge will be in contact will determine the material.
A copper alloy pressure gauge is suitable for low liability applications, but for high liability or high critical service applications, corrosion-resistant materials such as stainless steel or a nickel-copper alloy such as Monel are required.
The medium also affects the type of box fill used. Glycerin is the standard fill fluid for non-oxidizing environments, while highly reactive media requires an inert oil such as Halocarbon or Fluorolube.
5. P- Pressure
The question must be asked: what type of pressure should be measured?; relative pressure, absolute pressure or differential pressure? Second, what is the operating range of the application? Normally a pressure gauge should be selected whose range is twice the optimum working pressure, as this ensures the best performance.
Standard gauges can work up to 20,000 psi (1,600 bar), and special gauges can work up to 87,000 psi (6,000 bar). For low pressure measurements, a capsule manometer should be used to detect small pressure differences in units such as millibar (mbar), millimeters of water column (mmH2O), or ounces per square inch (oz/inch2).
Finally, what is the desired pressure range? Pressure gauges are available in a wide variety of measurement units, e.g. psi, bar, kPa, inH2O. All pressure gauges can be customized, with double scale, triple scale or custom scales, according to the needs of the application.
6. E – End (process connections)
Which endpoint or process connection is needed? The most common type is NPT. Then, for each type, the size of the connection must be defined, either ⅛”, ¼” or ½”. And finally, the location of the process connection; the two most common are rear or vertical.
7. D – Delivery days
The delivery time is something that must be kept in mind, because if several pressure gauges are needed in a short period of time, the options will be standard models in common nominal sizes that are already in stock. But if you can wait a few weeks, you will be able to get the exact pressure gauge you want with all the desired requirements.
Most common pressure gauges
There are different types of pressure gauges that adapt to different applications and needs. Among the most common pressure gauges, these five types stand out:
- The type C Bourdon tube manometer.
- The spiral, helical manometer.
- The diaphragm or capsule manometer.
- The digital pressure gauge (piezoelectric).
- The bellows pressure gauge.
Bourdon tube pressure gauge C.
This type of pressure gauge uses a curved tube, known as a Bourdon tube, to measure fluid pressure. The pressure of the fluid exerts a force inside the tube, causing it to expand or contract, which translates into a mechanical transmission of movement to a gear connected to an indicator needle that allows reading on a graduated scale on the face of the instrument.
Bourdon tube pressure gauges are ideal for low and medium pressure applications, such as in refrigeration and air conditioning systems, and are very accurate and stable. For high pressures (70 bar or greater) the spiral jet type is used.
Spiral and helical pressure gauge.
This type of pressure gauge uses a spiral or helix-shaped measuring device to measure the pressure of a fluid. This pressure exerts a force on the element, causing it to bend or stretch and resulting in a correction factor that is read on a graduated scale. Spiral or helical pressure gauges are suitable for low and medium pressure applications, such as in combustion systems, and are very efficient and stable.
Diaphragm or capsular pressure gauge.
Uses a flexible diaphragm or capsule system to measure pressure. The force is exerted on the diaphragm or capsule, causing it to deform, which manifests itself in mechanical transmission of movement to a gear connected to an indicator needle that can be read on a graduated scale. Diaphragm or capsule pressure gauges are ideal for low and medium pressure applications, such as in process systems.
Digital pressure gauge.
It is a modern and technological option to measure fluid pressure. This type of pressure gauge uses electronic (piezoelectric) sensors to measure pressure and displays the reading on a digital display. Digital pressure gauges are ideal for high precision applications and are very easy to read and use.
Bellows pressure gauge.
This type of pressure gauge uses a flexible bellows or membrane to measure fluid pressure. The pressure of the fluid exerts a force on the bellows or membrane, causing it to deform, which results in a mechanical transmission of movement to a gear connected to an indicator needle that can be read on a graduated scale. Bellows pressure gauges are ideal for low and medium pressure applications, such as in refrigeration and air conditioning systems.