Pressure tends to be pretty noisy, and since pressure gauges typically have some sort of spring return to zero, the needle can be made to oscillate pretty easily due to spring action. A mechanical resistance (damper, dashpot) is added to the gauge movement to cause a more stable needle reading.
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
Wika publishes the results of test with surprising results - mechanical vibration destroyed gauges with movement damping, but without liquid filling. The summary table is
I never put a pressure gauge on a pump unless it's liquid filled.
In gas or steam service you can get away with a non filled gauge in most cases, the exception might be on a compressor discharge where the high frequency vibration will shake a gauge to pieces. If its mounted off the line and connected with tubing it would probably be OK
This can also be achieved by adding a fixed or variable restriction to the gauge. A fixed is a batter practice...i have seen operators close off variable, locking in the pressure, then walking away. It keeps their unit running, but they sometimes forget they are putting production ahead of safety and equipment.
Jut pinching off the valve doesn't always work. Take the example of a pump, pinching off damps out the pressure fluctuations but does nothing for the mechanical vibration transfered along the pipe.
I have used these literally hundred of times on compressors, and never had an issue. the downside is that response time is hampered greatly. I have also used them on several pumps.
I wasn't trying to say snubbers don't work but when you are designing a new installation it's one more item you need to worry about.
Do you have the vendor include it with the gauge?
Does the vendor even have snubbers?
Do you give it a tag Number?
Do you put one on every gauge?
Does it show on the P&IDs, otherwise how does the contractor know to install one?
IMHO it's easier to specify a gauge with or without damping fluid, that's just one or two line items on the data sheet often at no additional cost.
Some clients have their own installation details but I haven't seen one asking for snubbers, not to say I won't.
Cheers
Roy
