In testing the Gammon Gauge, there are sometimes problems. These are usually manifested in the piston not traveling to the bottom of the scale. This is rare since most systems have at least 40 psi at the filter inlet.
The common reasons for problems are:
- Some people test on compressed air or nitrogen. You cannot do this with a piston gauge, liquid must be used. We can advise on how to do this.
- In some systems, the system cannot generate more than 30 psi and they have a 30 psi gauge. In such a case, the gauge can be converted to a 0-15 psi gauge by replacing the spring and scale.
- In some cases, the system pressure gauge may read a higher pressure than is present on the gauge inlet.
- Restrictions in the vent line from the Gammon Gauge test valve.
To properly test travel on a Gammon Gauge, you need more than 30 psi on the inlet. One reason is that the test valve doesn’t completely shut off the downstream pressure. Some pressure from the outlet sense line still gets through to the underside of the piston. Another reason is if the vent line is long and/or goes into a tank or port that has some small amount of pressure in it. For example, if the vent goes to the slop tank and it can hold a little pressure due to its pressure operated vent. An additional reason is if the vent line goes through a check valve (they always take a little pressure to open).
The easy way to detect such an issue is to disconnect the vent line from the relief valve on the Gammon Gauge tester.
There is one other possibility, that the pushbutton valve poppet has been distorted. We have seen this a couple of times, where the button was accidentally hit or pushed VERY, VERY hard. You can’t do this by simply pushing it, even if you try. But if you know you have 40 psi and you know the vent line is wide open and you still have this problem, replace the vent valve.
