Diagnostics of the technical condition of a modern car or industrial plant is impossible without accurate measurements. The centerpiece of this chain is often a manometer, a device that seems simple only at first glance. However, if you look at the dial, you can see many symbols, letters and icons, the value of which is critical for the safety and correctness of measurements.
Incorrectly selected or misread instrument can cause an emergency, especially when it comes to high pressure systems, such as: brakeway or fuel-stamp. Understanding the marking allows not only to choose the right tool, but also to notice its malfunction in time. In this article, we will discuss all aspects of labeling in detail.
It is important to realize that each character on the scale is not just a decor, but the result of strict standards of GOST or DIN. Ignoring this data when working with invasive environments or oxygen-carrying It could cause an explosion. Therefore, the ability to read the “language” of the pressure gauge is a must-have skill for any engineer or auto mechanic.
Basic types of scales and units of measurement
The first thing you look at when you look at the device is a digital scale. However, the units of measurement may vary significantly depending on the country of manufacture and the scope of the device. In international practice, as well as in most modern cars, the standard is the Bar (Bar) or Megapascal (MPa).
Often on the dials you can find a designation PSI (pound force per square inch). This is the standard for American machinery and specialized equipment. Confusion between units of measurement is one of the common causes of errors when pumping tires or setting up pneumatic systems. Always check what units your device is calibrated in.
Table of rapid translation of pressure units
1 Bar ≈ 14.5 PSI|1 MPa = 10 Bar|1 Atm ≈ 1.013 Bar|1 Kgs/cm2 ≈ 0.98 Bar
For accuracy of measurements, it is critical to consider the range of the scale. The working pressure should be in the range from 1/3 to 2/3 of the scale of the device. If the arrow is constantly "lying" at the beginning or "resting" at the end, the measurement error increases sharply, and the mechanism's resource decreases.
Accuracy classes and their marking
The figure in the circle or simply the numerical value on the front panel indicates the accuracy class of the device. This value shows the permissible percentage error of the measurement relative to the entire range of the scale. The smaller the number, the more accurate the device.
In automotive diagnostics and home use, accuracy classes are most common 1.5 and 2.5. This means that at a scale of 10 Bar, the error can be up to 0.25 Bar. For high-precision laboratory work or calibration, reference manometers with a class are used. 0.6 or 0.4.
⚠️ Note: Using a pressure gauge with accuracy class 4.0 to adjust the fuel system of the injection engine is unacceptable, since the price of division is too high for correct adjustment.
Over time, the spring mechanism may get tired, which leads to a shift in readings. If the pressureless arrow is not zero and the accuracy class requires perfect calibration, the instrument must be checked or replaced.
For most tasks in the service (checking the pressure of oil, fuel, tires), the best choice is devices of accuracy class 1.5 or 2.5.
Decoding of letter designations of the environment
One of the most important parts of the marking is the letter designation, indicating the type of medium the pressure gauge is designed to work with. The wrong choice can lead to corrosion of internal mechanisms or chemical reactions with a dangerous explosion.
The following abbreviations are most common:
- 🅱️ V or VM) - pressure gauges for work with aggressive, viscous media, often with a separator.
- 🅾️ K - Oxygen pressure gauges (oxygen gauges). Require degreasing and special lubrication that does not react with oxygen.
- 🅰️ And - pressure gauges for ammonia (ammonia). They have a stainless steel body and a specific design.
- 🚫 NZN - the body and parts are made of stainless steel, which is important for working with aggressive liquids.
Particular attention should be paid to oxygen manometers. On their scale must be the inscription “Oxygen”. It's oil-dangerous! The entry of even a microscopic drop of oil into an oxygen environment under pressure causes an instantaneous explosion.
For the automotive sector, designations for refrigerants (freon) are also relevant, if we are talking about the diagnosis of air conditioning systems. Such devices often have composite scales with color zones for different types of gases.
Connection schemes and threaded connections
Under the dial or on the side of the body is often applied schematic image showing the location of the fitting. This is critical when ordering a device, since the wrong model may simply not stand on the regular place.
The main types of connection:
- 📍 Radial (M) - The fitting is located at the bottom of the body. The most common option for stationary installation on pipelines.
- 📌 Axial (T) The rod is in the back, in the center. It is often used in instrument panels or where the gauge is mounted in the plane of the shield.
- 🔄 Rear-shifted - a variation of the axial connection, where the axis of the fitter is shifted relative to the center.
The size of the carving is also strictly regulated. In automotive and industrial technology, metric threads are the most popular M10x1, M12x1.5 and M20x1.5. In imported equipment, inch thread is often found G1/4 or NPT.
When installing a radial-connected pressure gauge on vibrating sections of the pipeline, it is recommended to use a pulse tube or damper to protect the mechanism from shaking.
Climate performance and degree of protection
The operating conditions dictate their requirements for the design of the device. The climatic designation indicates a temperature range in which the declared accuracy and performance are guaranteed.
The standard execution is indicated as U2 (moderate climate) and involves working at temperatures from -45 to +60 degrees Celsius. For harsh conditions (for example, for equipment operating in the north or in the open air) the execution is applied. UHL2 or UHL4It can withstand extremely low temperatures.
| Designation | Climate | Temperature range (exemplary) | Application |
|---|---|---|---|
| U2 | Moderate. | -45...+60 °C | Premises, sheds |
| UHL2 | Moderate and cold | -60...+60 °C | Open air |
| T2 | Tropical | -10...+60 °C | High humidity |
| OM2 | Ship-to-ship | -50...+60 °C | Maritime vessels |
The degree of protection is indicated by the marking IP (Ingress Protection). For automotive pressure gauges that may be exposed to water and dust, the minimum acceptable standard is IP54. The number 5 means protection from dust, and 4 - from water splashes.
If the pressure gauge is installed on the street or in the wash area, choose models with protection class IP65 and above to prevent moisture from entering the mechanism.
Additional symbols and special performances
In addition to the basic characteristics, special signs may be present on the dial indicating additional functions or design features. For example, a letter G. The labeling often indicates the presence of glycerol filling.
Glycerin (or silicone oil) inside the housing acts as a damper. It extinguishes vibrations and prevents the shaking of the arrow, which is especially important for pressure gauges installed on engines or compressors. Without such a liquid, the arrow will quickly break the glass from the inside.
You can also find the color code of the case, which duplicates information about the environment:
- 🟢 Green. - Oxygen (oil hazard).
- 🟡 Yellow - Ammonia.
- 🔵 Blue. - acetylene.
- ⚪ White - flammable gases.
Some modern models are equipped with a locking arrow (maximeter), which records the maximum achieved pressure value. This is convenient for diagnosing peak loads in the system that last a fraction of a second and are not visible to the eye.
⚠️ Warning: If you see a crack in the glass or glycerol-filled pressure gauge body, stop using immediately. The leaking liquid can damage the paint coating of the car.
Checklist of the correct selection of the manometer
In order not to make a mistake when buying or replacing a measuring device, you need to consistently check all the parameters. Using an inappropriate pressure gauge is a direct path to incorrect diagnosis and potential repair of nodes.
☑️ Algorithm for manometer selection
Be sure to pay attention to the release date and the date of the last verification if the device requires certification. For automotive needs, factory verification is sufficient, but for industrial equipment, periodic checks may be required in metrological services.
A high-quality pressure gauge should have a clear, unblurred scale, easy to read from a distance. If the numbers on the dial are erased or the spraying is bad, it is better not to use such a device, since the risk of reading the reading error is too great.
Frequently Asked Questions (FAQ)
What does the red line on the pressure gauge mean?
The red line or red zone on the scale indicates the maximum permissible pressure, which is prohibited to exceed. Operation of the system in this area can lead to a pipeline rupture or equipment failure. The work area is usually up to 75% of the maximum scale.
Can I use a water pressure gauge to measure oil pressure?
Technically, it is possible if the pressure ranges are the same, but this is not recommended. Oil gauges often have special internal protections or filling adapted to the viscosity of the oil. In addition, the material of the internal springs can be different for different environments.
Why does the pressure gauge not go back to zero?
This is a sign of a faulty spring mechanism (deformation of the Bourdon tube) or a jamming of the axis. It can also be caused by residual pressure in the system. If after the pressure relief the arrow is not at zero, the device shows incorrect data and requires replacement.
How often should I change the pressure gauge on the car?
Manometers do not have a strict shelf life, but are subject to replacement in case of damage, leakage or if the error of readings exceeds the declared accuracy class. In conditions of aggressive vibration, the life of the device can be 1-2 years of active operation.
What is the difference between absolute and excess pressure on the pressure gauge?
Most car pressure gauges show excessive pressure (the difference between system pressure and atmospheric pressure). Absolute pressure takes into account atmospheric pressure and is used for specific tasks (e.g., vacuum systems or meteorology). On the absolute pressure scale is often the letter "A" (kgf/cm2A).