The free end of the spring in the pressure gauge is closed, and it drives the sector gear to rotate through the tie rod. During the pressure measurement, the spring tube is deformed under the action of the measured pressure, so the free end of the spring tube is displaced. The displacement is proportional to the measured pressure, causing the pointer to deflect and indicate the pressure value on the dial. If there is atmosphere in the case, the pressure measured by the pressure gauge is positive or negative; if the case is sealed and evacuated, the pressure measured by the pressure gauge is the absolute pressure.
When the spring tube pressure gauge is equipped with an isolation device, it can still measure the pressure of the medium with high temperature or corrosive, viscous, crystalline and dusty medium. In the elastic pressure measuring instruments with high accuracy (such as above 0.25 grade), the elastic elements are mostly made of constant elastic alloy or quartz glass. Jewel bearings or rolling bearings are embedded in the shaft holes of the transmission mechanism. The scale of the dial is long, and some can also display numbers.
Factors affecting the accuracy of pressure gauge measurement
First, the influence of temperature
Pressure measurement is the effect of pressure that deforms the spring elbow.
If the temperature of the medium entering the spring elbow is high, the temperature will also deform the elbow. And the high temperature medium acts on the spring elbow for a long time, and it will also cause permanent deformation of the elbow.
All of these will adversely affect the measurement.
Preventive measures: Between the pressure gauge and the drum, different types of water storage elbows are installed to accumulate condensate and prevent steam from directly entering the spring elbows.
Second, the effect of freezing and vibration
The pressure gauge is installed outside the boiler and is greatly affected by external conditions. If the outside temperature is too low, freezing, or various vibrations from the boiler body and the pressure gauge, it will affect the sensitivity and accuracy of the pressure gauge pointer.
Precautionary measures: one is to install a thermal insulation device; the other is to install a buffer device, such as a three-way cock is a kind of anti-shock device.
Three, the impact of overload
Elastic components such as spring elbows and hairsprings in pressure gauges are often at or near their limits. Working for a long time will lead to weakening or loss of elasticity, and even permanent deformation.
If the pressure gauge pointer is often close to or greater than 2/3 of the full scale of the dial, it is detrimental to the long-term operation of the pressure gauge.
Prevention method, when the pressure gauge is first selected, the range should be selected reasonably, and the working pressure is best at 1/2 of the range. Secondly, we must strictly prevent the boiler from operating at overpressure.