On the low-cost end of the snubber spectrum is the porous disc type (also known as a “filter type”). The fixed disc creates a semi-permeable barrier between the incoming pressure and the pressure gauge’s orifice. The pressure meets that disc and has its force distributed through the metal mesh, slowing it so that it will not harm the gauge. The pressure rises gradually, so that the gauge doesn’t jump a gear or burst a bourdon tube.
The porous disc design allows consistent pressure at low speeds, though, so that the gauge’s readings are not affected by the filtering material.
The downside of a porous disc snubber is that it can become clogged, depending on the process being measured. In that case, the readings would be affected and the snubber would have to be cleaned by flushing it from the gauge side with a solvent.
A piston-type snubber has a little more advanced design that is often self-cleaning. Often designed in two pieces, the piston inside the snubber moves freely, acting as a barrier to the rapid increase in pressure. When pressure increases too rapidly, the piston is forced against the orifice leading to the gauge, stemming the flow for milliseconds. As long as it is just a spike, that should be long enough to avoid damage to the gauge.
This type of snubber can usually be “tuned” to meet a process’s needs by using easily changed pistons of varying sizes. The diameter of the piston and its clearance within the snubber determine the rate of “dampening” that occurs.
A third “adjustable” snubber takes that fine tuning to another level. Many use a combination of a ball check to block surges and a kind of choke valve to smooth out the flow of material into the gauge. The ball check acts a lot like the piston-type snubber in that it is a passive element until a rapid change in pressure pushes it into action.
Even adjustable snubbers without the ball check can be effective in smoothing out a lot of pulsation, thanks to the integrated choke valve, which will only allow so much fluid through at one time. In a pinch, a regular needle valve could be substituted, but that is not necessarily a permanent solution to the above customer’s problem. In that case, it was a major momentary spike in pressure that damaged the gauge and a needle valve alone wouldn’t have completely arrested the surge.
Many adjustable snubbers also have the benefit of leak-tight shutoff, allowing the operator to remove the gauge for repair or removal.
Pressure ratings for snubbers can range from 1,000-20,000 psi, depending on type, size and the material used. Be sure to consider how much pressure might be introduced through spikes, water hammers and pulsation, as well as the media being measured, when deciding on the right snubber.