What a pressure gauge measures and how to use it

What do you need a pressure gauge for, types, rules of choice and use

Servicing a car is impossible without some obligatory devices. This list includes pressure gauges, which are used to measure the pressure in the tires. Experienced drivers are familiar with this device. Beginner drivers still have to get acquainted with it. It is necessary to do this, because the safety of movement depends on the pressure in the tires.

What is the purpose of the pressure gauge

Car tires constantly maintain the pressure, which must be at a certain level. The safety of movement depends on it, first of all. The pressure in tires may decrease during the operation of the car, its level should be periodically checked and, if necessary, increase. To measure this indicator allows a manometer for tires.

If everyone understands what the pressure gauge measures, then we can move on. We have a lot to talk about, learn how to use this device and choose correctly.

Types of pressure gauges, their pros and cons

Devices to measure the pressure inside the wheel are produced by many manufacturers. They are presented in several varieties, which have many differences. Further we will study what kind of pressure gauges are, we will dwell on their advantages and disadvantages, we will study the principle of operation, which also differs depending on the variety of the device.

Mechanical devices

The simplest, most accessible and “ancient” kind of mechanism. Mechanical pressure gauge consists of a dial with a scale on which the actual pressure level is displayed. Characterized by simplicity and reliability. This device will not fail, because, in fact, there is nothing to break in it. Despite such simplicity and availability of the device readings are accurate. Buy such a pressure gauge can each driver, on the budget this purchase is not particularly affected.

The disadvantages include sensitivity to moisture and duration of measurements on four wheels. Some drivers may have difficulty reading the measurements obtained. Also the results in some cases require verification.

Various models feature mechanical pressure gauges. Some have a valve that can be used to bleed air from an over-pumped wheel. It is very convenient when you can simply press a button and bleed the excess air from the wheel, bringing the pressure reading back to normal.

Rack and pinion pressure gauges.

They are less popular than the previous variety, but still some motorists lying in the glove compartment, trunk or garage. Their design resembles a pen, the basis is a spring, which has the shape of a cylinder. They are reliable, compact and affordable.

The disadvantages include a fragile design and not very convenient to use. Therefore, not all drivers are satisfied with rack pressure gauges, the more so, they have a decent replacement in the form of mechanical and electronic devices.

Electronic devices

Their popularity is increasing, and they are steadily replacing the previous two varieties. Even the high cost does not embarrass motorists. It is convenient to use electronic pressure gauges to measure the pressure in tires, with them the time of measurements is reduced at times. The list of advantages should also include high accuracy. More expensive models are equipped with additional functionality.

They can not be called an ideal choice, because the electronics are afraid of frost. This affects the accuracy of measurements. It is not always possible to take measurements in a warm garage, so the relevance of buying a digital pressure gauge in some cases is questioned.

Systems of pressure control

You can not bother with the pressure gauge and set a special system to check the pressure in tires. Such technology in science is called TPMS. There are two varieties:

1. Direct systems measure directly from the wheels. They are very popular and are used by many car manufacturers. There are two varieties of direct tire pressure monitoring systems:

• OEM options;
• Non-standard universal sensors, which can be installed on any car.

1. Indirect models read the readings from ABS sensors. If the wheel is flat, its radius will be less than normal. Such systems are becoming a thing of the past and more and more manufacturers refuse them. The reason for this situation is a large error, which is also accompanied by malfunctions.

How to choose the right pressure gauge

Before every motorist sooner or later there is a need to choose a pressure gauge. Do not choose the first caught model, which attracted the appearance or cost. Focus on the performance and a number of important indicators. Our tips should alleviate the agony of choice.

1. First of all, all the performance characteristics of the device are taken into account:

• measuring range;
• accuracy class;
• units of measurement;
• related options;
• operational characteristics.

1. For infrequent use, you can buy an inexpensive, most basic model. But you should not be tempted by outright “consumer goods” either. For professional work requires a more serious unit with a solid body and reliable stuffing.

Separately, let’s look at some of the performance characteristics previously mentioned.

1. The accuracy class is divided into three categories. The first is the most inaccurate, the error can range from 1 to 0.5. For the second class, a deviation from 0.5 to 0.1 is acceptable. Devices of the third class are the most accurate, respectively, and the most expensive. The error here does not exceed 0.05. If the device is chosen for yourself, you can limit yourself to the second accuracy class. For professional work, a more accurate technique is required.
2. Not all car owners pay attention to the units of measurement, and then regret it. There are several options: bar and kg/cm2 are most common, sometimes Pascals (mPa, kPa) can be used. Owners of passenger cars will find it easier to work with readings in bar.

And now we present to your attention the rating of manufacturers who are engaged in the production of such measuring equipment. After studying it you will know exactly what pressure gauge is better.

1. Of course, our rating will be headed by the German devices from the company BMW. You can find both mechanical and electronic in the markets. Both options are very reliable, the accuracy class is medium.
2. Among the budget models, CEM TP-5 is worth mentioning. The measuring range is extensive, the use is versatile and simple, pleasant ergonomics – a good option for home use.
3. The Chinese can do well if they want to. This is confirmed by the CARPOINT model. The only thing missing is a backlight that would make it possible to use this device at night. On the other hand, you don’t have to change batteries as often.
4. The choice of specialists can be pressure gauges from the company “Berkut”. The most successful model is the Digital MAX, which entices the user with a wide range of functions. Due to the built-in memory, you can track the increase in the existing defect.

How to measure pressure correctly

Pressure gauges are different, therefore, and the principle of their work is different. Use a pressure gauge is not difficult, no matter what type of mechanism was not in your hands. And that the data differed high accuracy and did not have to make repeated measurements, it is necessary to adhere to certain rules:

1. Measurements should be carried out on completely cooled wheels. After moving the car, you need to wait at least 3 hours. This is due to the relationship between pressure and temperature of gases that are in a confined space. In a heated wheel, the pressure will be 15% higher from its real value. In winter, the measured value will be underestimated by about 10%.
2. Inspection should be regular. On worn and heavily used tires, it is advisable to measure before each trip. In other cases, it is prudent to check every week.
3. Digital units may measure when the system is disconnected from the nipple. This situation is due to recalibration. In such situations, it is the final reading that will be most accurate.
4. In the case of tires that differ from standard tires, reference should be made to the tire manufacturer’s recommendations.
5. It is correct to measure in a car that is not loaded. With a load, the pressure should be higher than normal.
6. For driving on sand, it is possible to make the pressure slightly lower than the norm. In this case, the car will be easier to move on such a road, traction with the road will become more confident and the cross-country capability of the vehicle will increase. Rocky ground, snowdrifts and puddles are not the reason for experimenting with the rubber indicators.

Do not neglect the purchase of a pressure gauge, because you need to constantly monitor the pressure in tires. Low, as well as high, will reduce the safety of movement.

What does the pressure gauge measure and what pressure it shows

No modern building does not do without a heating system. And for its stable and safe operation requires accurate control of fluid pressure. If the pressure within the hydraulic schedule is stable, the heating system is working properly. However, when it increases, there is a risk of rupture of the pipeline.

A drop in pressure can also lead to negative consequences such as cavitation, i.e. air bubbles forming in the pipe, which in turn can cause corrosion. Therefore, to maintain normal pressure is essential, and thanks to the pressure gauge is possible. In addition to heating systems, such devices are used in a variety of areas.

Description and purpose of the pressure gauge

A pressure gauge is a device that measures pressure levels. There are types of pressure gauges that are used in a wide variety of industries, and, of course, each of them is designed for a different pressure gauge. For example, we can take a barometer – a device designed to measure the pressure of the atmosphere. They are widely used in engineering, agriculture, construction, industry and other areas.

These devices measure pressure, and this concept is extensible, at least, and this value also has its own varieties. To answer the question of what kind of pressure the pressure gauge shows, it is worth considering this indicator as a whole. It is a value that determines the ratio of the force acting on the unit surface area, perpendicular to this surface. Virtually any technological process is accompanied by this value.

Types of pressure:

• atmospheric – the pressure of the earth’s atmosphere, which is created by the mass of the air column;
• absolute pressure – it is an indicator, counting which, taking into account the atmospheric pressure, starts from zero;
• excessive – by excessive we mean the difference of the two indicators of the atmospheric and absolute;
• vacuum or, in other words, discharged – on the contrary, is the difference of the absolute and the atmospheric or barometric value;
• differential – it is the difference between two measured indices, which have no relation to natural indices.

There are certain types of gauges for measuring each of the above types of indicators.

Classification of devices

Types of pressure gauges are distinguished on two grounds: by the type of indicator they measure and by the principle of operation.

According to the first feature, they are divided into:

• Instruments designed to measure atmospheric pressure, otherwise they are called barometers;
• instruments measuring gauge and absolute;
• vacuum gauges, designed to measure the difference of atmospheric and absolute pressures;
• Pressure gauges, measure small (up to 40 kPa) overpressure;
• tachometers, a type of vacuum gauge that measures the excess pressure of the upper limit of 40 kPa;
• differential pressure gauges, which measure pressure differences.

They work on the principle of balancing the pressure difference with a certain force. Therefore, the device of pressure gauges is different, depending on how exactly this balancing occurs.

According to the principle of operation, they are divided into:

• liquid, balancing the pressure difference in such devices is due to the hydrostatic pressure of the liquid column, the device uses the principle of communicating vessels;
• spring instruments have a simple design, and are widely used to measure the pressure of the medium in a wide range;
• diaphragm, based on pneumatic compensation, pressure balancing is due to the elastic force of the diaphragm box
• electro-contact ones, are used in automatic control and signaling systems, as they can be used to regulate the measured medium thanks to an electro-contact mechanism built into the body;
• differential are used to measure the level of liquids under pressure by means of diaphragms of liquid, steam and gas flow.

By purpose, there are such types of pressure gauges as:

• General instruments are used to measure the head of liquids, gases and vapors that are chemically neutral to copper alloys;
• oxygen, they are produced in blue cases with the indication of O2 on the dial and are used to measure oxygen pressure in cylinders or vacuums;
• acetylene ones are used to control the overpressure of acetylene;
• reference instruments are used to check other instruments as they are very accurate;
• ship instruments are used in ships and maritime transport;
• railroads are used in railroad transport;
• self-recording ones have an in-built mechanism that allows reproducing the result of the work on paper.

Design and principle of operation

The device of the pressure gauge can have a different design depending on the type and purpose. For example, a device that measures the pressure of water, has a fairly simple and straightforward design. It consists of a body and a scale with a dial, which displays the value. The body has a built-in tubular spring or diaphragm with a holder, a tripco-sector mechanism and a resilient element. The instrument functions on the principle of pressure equalization through the force of the shape change (deformation) of the diaphragm or spring. The deformation, in turn, drives a sensitive elastic element, the action of which is displayed on a scale with an arrow.

Liquid pressure gauges consist of a long tube which is filled with liquid. In the tube with the liquid is a movable plug, which is affected by the working medium, the force of the head should be measured according to the movement of the liquid level. Pressure gauges can be designed to measure the difference, such devices consist of two tubes.

Piston ones – consist of a cylinder and a piston located inside. The medium in which the pressure is measured acts on the piston and is balanced by a weight of some magnitude. When the index changes, the piston moves and actuates an arrow that shows the pressure value.

Thermoconductive ones consist of a filament that is heated when an electric discharge is passed through it. The principle of operation of such instruments is based on the decreasing thermal conductivity of the gas with pressure.

The Pirani gauge is named after Marcello Pirani, who first designed the device. Unlike thermally conductive ones, it consists of metal wiring, which is also heated during the passage of current through it and cooled by the working medium, namely gas. As the pressure of the gas decreases, so does the cooling effect, and the temperature of the wiring increases. The value is measured by measuring the voltage in the wire while the current is flowing through it.

Ionization devices are the most sensitive devices that are used to calculate small pressures. As the name of the device implies, its principle of operation is based on the measurement of ions, which are formed by the effect of electrons on the gas. The number of ions depends on the density of the gas. However, ions are of a very unstable nature, which depends directly on the working medium of the gas or vapor. Therefore, a different kind of McLeod gauge is used for refinement. Refinement is done by comparing the readings of the ionization gauge, with the readings of the Mac Leod instrument.

There are two types of ionization devices: hot cathode and cold cathode.

The first type was designed by Bayard Allert, consists of electrodes that operate in triode mode, and the filament acts as the cathode. The most common type of hot cathode is the ion gauge, which has a small ion collector built into its design in addition to the collector, filament and grid. Such gauges are very vulnerable, they can easily lose calibration, depending on operating conditions. Therefore, the readings of these instruments are always logarithmic.

Cold cathode also has its own varieties: integrated magnetron and Penning gauge. Their main difference is the position of the anode and cathode. There is no filament in the design of these devices, so they require a voltage of up to 0.4 kW to operate. Using such devices is not effective at low pressure levels. Because they may simply not work and do not turn on. The principle of their work is based on the generation of current, which is impossible in the complete absence of gas, especially for the Penning gauge. Because the device only works in a certain magnetic field. It is necessary to create the desired trajectory of the ions.

Color coding

Pressure gauges that measure gas pressure have colored cases, they are specially painted in different colors. There are several basic colors that are used to color the case. As an example, pressure gauges that measure oxygen pressure have a blue body with the O2 designation, ammonia pressure gauges have a body colored yellow, acetylene pressure gauges are white, hydrogen pressure gauges are dark green, and chlorine pressure gauges are gray. Devices that measure the pressure of flammable gases are painted red, and non-flammable – black.

Advantages of use

First of all, it is worth noting the universality of the pressure gauge, which lies in the ability to control the pressure and maintain it at a certain level. Secondly, the device allows you to get accurate indicators of the norm, as well as deviation from them. Thirdly, the availability of almost anyone can afford to purchase this device. Fourthly, the device is able to work stably and smoothly for a long time, and does not require special conditions or skills.

The use of such devices in fields such as medicine, the chemical industry, the automotive industry, maritime transport, and others requiring precise pressure control makes the work much easier.

Accuracy class of the device

There are many pressure gauges, and each type is assigned a certain accuracy class according to the regulations of GOST, which means the allowable error expressed as a percentage of the measuring range.

There are 6 accuracy classes: 0.4; 0.6; 1; 1.5; 2.5; 4. Each type of pressure gauge also differs. The above list refers to working pressure gauges. For spring devices, for example, the following values correspond to 0.16; 0.25 and 0.4. For piston ones, 0.05 and 0.2 and so on.

The accuracy class has an inversely proportional relationship to the diameter of the instrument scale and to the type of instrument. That is, if the diameter of the scale is larger, the accuracy and precision of the pressure gauge decreases. The accuracy class is conventionally denoted by the following Latin letters KL and CL, which can also be found on the instrument scale.

The error value can be calculated. Two indicators are used for this: the accuracy class or KL and the measuring range. If the accuracy class (KL) is 4, the measuring range is 2.5 MPa (Megapascal) and the error is 0.1 MPa. The formula is calculated as the product of the accuracy class and measuring range divided by 100. Since the error is expressed as a percentage, the result must be converted to a percentage by dividing by 100.

In addition to the basic form, there is an additional uncertainty. While the first type is calculated using ideal conditions or natural values influenced by the design features of the instrument, the second type depends directly on the conditions. For example, temperature and vibration or other conditions.