We’ve all been there.
Your pressure tank’s instrument gauge that was operating just fine yesterday is now stuck at 30 psi.
Thunk Thunk Thunk! (That’s you tapping the gauge with a rather large wrench just to make sure a good rapping won’t bring it back…)
This will be the third time this year you’ve had to replace the foul thing! Now what?
Glad you asked.
Here’s what you need to know.
First, you need to make sure the wetted parts – that is, the parts of the gauge that will come into contact with media – are compatible.
Many of the gauge manufacturers have online charts that list what materials their gauge is constructed of along, with the media they are compatible with.
An example of this would be Ashcroft’s corrosion guide.
Sometimes, though, just having compatible materials is not adequate.
Your only option in that case is to isolate the gauge from the media.
There are many ways to accomplish this. The simplest way is to use a coil siphon tube.
This tube is installed between the gauge and the tank the media is located within. This type of isolation device is commonly used to isolate a pressure gauge from direct steam. The loop in the pipe is filled with water, thereby isolating the gauge from direct contact with steam.
Another common option is the use of a diaphragm seal. This type of seal includes a flexible type membrane as part of its design. The membrane allows your media’s pressure effects through the membrane but not the media itself.
Again, you will need to choose a membrane material that will be compatible with the media you are using in your manufacturing process.
Other types of isolation devices are isolation rings, gauge guards, or isolation spools.
A mistake at this stage in the game can cost you time and money.
When you’re having an issue, the best thing you can do is seek the advice of ASME Code tank experts who understand the tanks from design to repair.
Which type of isolation devices have you worked with?
