1. Opening a vent to release pressure build-up
This is the simplest technique. Due to changes in temperature and altitude, pressure inside the pressure gauge will build up and affect the needle settings to zero. You can correct this by just opening the vent to release the pressure.
Do not forget to return or re-seal the vent. The oil may leak and may damage the gauge.This is the simplest of all the adjustment techniques that is usually applicable to most oil-filled and permanently sealed types of analog pressure gauges. If this technique does not fix the problem, then a replacement is the only fix.
2. Opening the Pressure Gauge Protective Glass (or plastic cover) then remove the needle.
For non-oil-filled gauges, it is not permanently sealed (most oil-filled gauges are permanently sealed where adjustment or repair is not possible).
But in some cases where it can be opened, remove first the oil inside before removing the glass cover. You need an extra oil replacement just in case.
If you are wondering what is the liquid filled inside the pressure gauge is, it is called glycerine or silicone oil. It is important to replace or refill the pressure gauge oil when removed or if the oil has been drained because of a leak.
What are the advantages of oil oil-filled pressure gauge? Below are some of the reasons why we need to maintain the oil-filled pressure gauge:
Oil-filled pressure gauges are more protected from harsh environmental factors and moisture or water condensations. Some pressure gauge mechanical parts get stuck from dust and corrosion build-up resulting in wrong readings, or worse, damage.
Glycerine Oil-filled pressure gauges are also protected from strong vibrations. Strong vibrations affect the mechanical components. Some needles are getting removed or broken because of these strong vibrations.
Since the liquid-filled pressure gauge can resist strong vibration, the displayed readings of the needle are more stable, making it easy to read, thus, increasing the accuracy of the pressure gauge.
Glycerine or silicone oil acts as a lubricant for the mechanical parts especially for the needle pointer making it move smoothly.
In some cases where releasing the pressure build-up cannot solve the problem, we can perform the below adjustment by opening the pressure gauge through the removal of its protective cover and removing the needle pointer. With this method, we can correct the zero and span shift of the instrument when it occurs.
A. To correct the Zero Shifts:
Once the cover is removed, perform below steps:
1. Pull the needle using the needle puller (see below).
2. Once the needle is removed, position it on the zero scales then push to return.
3. Verify the reading by supplying pressure
How to perform pressure gauge verification? Read on …
B. To correct Span Shift:
Once the needle is removed, perform the following:
1. connect the pressure gauge to a known pressure source (the Electronic Deadweight Tester or PR235 with a set of pressure modules)
2. Generate a pressure of about 50% of its Full scale. Once the pressure is set, return the needle to the same value as the supplied pressure. For example, generate a 100 psi pressure from the reference standard, then fix the needle on the 100 psi scale reading on the pressure gauge.
3. Perform verification to ensure that it is now within the accepted range.
Most of the time, Just performing either A or B solves the problem.
3. Adjusting the knob at the lower side of the pressure gauge
Some pressure gauges have an adjustable knob on the lower side of the body. This is a diaphragm-type pressure gauge that is usually used in water treatment piping.Just remove the lock then the knob will freely turn to adjust the needle.
4. Adjusting the screw located inside the pressure gauge mechanism
Some pressure gauges have an adjustable screw inside the body, at the back of the needle, or within the dial face. This type of gauge is used in gas lines.
Access the screw inside the gauge by removing the cover. Turn the screw either clockwise or counterclockwise to return the needle to zero position.
5. Adjusting the screw located at the gauge needle pointer
This applies to some pressure gauge that has an adjustable screw integrated on the needle itself. Once the cover is removed, use a screwdriver and carefully turn the screw to position the needle. See the figure above or watch the video below.
Based on the photo above, I have shown you the location of the screw and the position of the screwdriver, but during the rotation of the screw, you need to hold the needle to rotate the screw and perform the adjustment.
You need to be more careful in this type of adjustment. the needle is connected with the spring inside and it is very sensitive. A strong force while rotating the screw can damage the whole part or pressure gauge.
