Why Hydraulic Systems Destroy Pressure Sensors: Water Hammer, Pressure Snubbers and Overload Ratings
When sensors repeatedly fail despite normal steady pressure, investigate unrecorded transients as well as corrosion, vibration, mounting stress and electrical faults. Water hammer and pulsation can damage a diaphragm. Check dynamic pressure and range-specific limits before selecting snubbing or a larger range.
Where the spikes come from
| Source | Mechanism | Peak characteristics |
|---|---|---|
| Water hammer | Fast valve closure or pump start/stop converts the kinetic energy of moving liquid into a pressure wave | Several times working pressure, lasting milliseconds |
| Directional valve shock | Valve switching, cylinder reaching end of stroke | High frequency and repetitive; causes fatigue |
| Piston pump ripple | Pump output ripple superimposed on steady pressure | Low amplitude but continuous fatigue loading |
| Sudden load change | Starting or stopping a suspended load, cylinder stalling | Single event, high amplitude |
What all of these share is extremely short duration. A conventional pressure gauge or a PLC sampling slowly will usually miss them entirely, while the diaphragm has already absorbed the full impact. That is why the complaint is so often “the system shows normal pressure, but the sensor failed”.
Reading overload and burst pressure
Overload is a withstand rating under stated conditions; burst pressure is a structural safety boundary, not normal operating pressure. Dynamic shocks also require pulse duration, repetition and fatigue assessment. A static overload number is not a complete repeated-water-hammer validation.
| Range (bar) | Overload (bar) | Overload factor | Burst (bar) |
|---|---|---|---|
| 1 | 10 | 10x | 50 |
| 2 | 10 | 5x | 50 |
| 5 | 25 | 5x | 50 |
| 10 | 50 | 5x | 300 |
| 20 | 100 | 5x | 300 |
| 30 | 150 | 5x | 300 |
The table above is from the RS WA30 outdoor transmitter, built around 5x overload for fire mains and pump rooms where water hammer is routine. On the high-pressure side, RS PM400-E varies by range: 5x at 0-100 bar, 3x at 0-160 and 0-250 bar, and 2x at 0-400 bar (800 bar overload, 1200 bar burst).
What a pressure snubber does
A snubber restricts or damps the rate of pressure change reaching the sensor. Its effect depends on medium, orifice and installation, and it changes dynamic response. Particles or viscous fluids may clog small passages; choose a maintainable compatible design and verify both steady readings and response.
A snubber changes dynamic response. Closed-loop control and peak recording need bandwidth validation. Even trend or level measurements should be checked for lag, blockage and steady-state error; slow-variable duty is not automatically unaffected.
Three ways to configure one
| Form | Description | Best for |
|---|---|---|
| Integrated snubber | Built into the pressure port at the factory; most compact | High-pressure pulsation duty; used on RS PM400-E and RS PC350 |
| Optional internal snubber | Specified at order time via the model code | Uncertain duty or cost-sensitive projects |
| External snubber | Added in the field ahead of the port | Retrofits and unusually severe spikes |
RS PM400-E lists an integrated buffer, and RS PM160-E offers an optional pulse snubber. Current RS PC350 information applies the integrated buffer to the pressure-port version; do not assume the bare core has the same feature. Check medium, response and ordered construction for each.
When to assess a snubber
- The system has fast-acting solenoid or shut-off valves and the sensor is mounted nearby.
- The sensor sits near a pulsation source such as a pump outlet or cylinder port.
- The same model has failed repeatedly on site while pressure records look normal.
- Working pressure is already close to full scale and a larger range is not acceptable.
- Particles or cavitation: first assess medium and pressure-port compatibility. A small-orifice snubber may clog and is not a default solution for every such duty.
- Long-term stability: assess temperature, medium, mechanical shocks and maintenance interval together. An annual drift target alone does not determine whether a snubber is needed.
A second layer: fault signalling
Fault output provides diagnostics; it does not replace mechanical overload protection. Confirm clamp levels, fault thresholds and reset behaviour for the selected PM400-E range and output. For example, the 0–400 bar version lists 800 bar overload, so a generic “3× full scale” rule is not safe.
A persistent fault may involve overload, an internal fault or wiring/supply problems. It does not identify the cause by itself. Isolate and investigate through the diagnostic procedure; replace confirmed damaged devices and do not simply reset an unexplained fault and resume service.
Selection checklist
| Item | How to verify |
|---|---|
| Working pressure and spikes | Record dynamic pressure, pulse duration and repetition; steady-state pressure is insufficient |
| Overload covers the spike | Check the per-range table — the factor drops on higher ranges |
| Burst pressure margin | Not an operating limit; check safety boundaries and project requirements |
| Snubber required? | Assess medium, clogging risk, pulses and response requirements |
| Response-time impact | Weigh against closed-loop or fast-capture requirements |
| Long-term stability | Confirm figures such as 0.10 % FS per year suit the maintenance interval |
Next step
Record the pressure trace, repetition, medium and installation position, then check the range-specific overload table. Repeated failures may also involve corrosion, cavitation, vibration, supply or mounting stress. Photos and measurement records support a systematic investigation.
More answers in the FAQ.
Related documentation: downloads page
Specifications: View WA30 datasheet (PDF) · Download PDF · View PM400-E datasheet (PDF) · Download PDF
Related products and documentation: RS PM160-E · RS PC350