A pressure snubber is installed between a pressure source and a gauge or transmitter to dampen pulsations, spikes, and water hammer.
Without a snubber, repeated spikes fatigue the Bourdon tube or sensing diaphragm, causing premature failure, pointer oscillation, and zero drift.
This guide covers the main types (porous, piston, orifice), selection criteria, and the orifice sizing calculation. See the pressure transmitter remote seal guide for protecting transmitters from process conditions.
A pressure snubber restricts the flow path to the sensing element. A sudden spike must accelerate a large fluid volume through a tiny restriction, absorbing its peak energy. Static pressure equalises correctly because it has unlimited time.
Pressure Snubber Working Principle
A pressure snubber acts as a low-pass filter. The restriction is the resistance and the gauge cavity volume is the capacitance in an RC-equivalent system. High-frequency spikes are attenuated; low-frequency and steady-state pressure passes through unchanged.
Passing a spike through a tiny orifice requires accelerating a large fluid mass, consuming more energy than the spike contains. The peak is absorbed. This is the same principle used in pneumatic accumulators and RC filter circuits.
Pressure Snubber Types Explained
1. Porous (Sintered) Snubber
A sintered porous disc (316 SS, bronze, or Hastelloy) is pressed into the snubber body. The tortuous micro-channels provide hundreds of tiny flow paths in parallel, creating high resistance to rapid flow while allowing static pressure to equalise.
2. Piston (Adjustable) Snubber
A spring-loaded piston with a central drilled orifice (0.3 to 0.8 mm) sits in the body. During a spike, the piston closes a bypass port, leaving only the small orifice open.
During steady state, the spring holds the bypass open for fast pressure transmission. The orifice can be adjusted or replaced in the field.
3. Fixed Orifice Snubber
A single drilled or jewel orifice (0.3 to 0.8 mm) is pressed into the body with no moving parts. This is the simplest and most reliable snubber type. The orifice diameter is fixed at manufacture and cannot be changed without replacing the snubber body.
Pressure Snubber Types: Comparison
| Parameter | Porous (Sintered) | Piston (Adjustable) | Fixed Orifice |
|---|---|---|---|
| Damping mechanism | Tortuous micro-channels through sintered metal disc | Spring-loaded piston closes bypass port on spike; small central orifice remains open | Single small-diameter drilled or jewel orifice in body |
| Moving parts | None | Yes: spring and piston | None |
| Static pressure response | Slow: minutes in fine-grade elements | Fast: bypass port open during steady state | Moderate: depends on orifice size |
| Spike damping | Excellent | Good | Good |
| Plugging risk | High: fine pores block with particulate or viscous fluid | Low: larger piston bore, piston clears the seat on each cycle | Medium: single orifice can plug with large particulate |
| Field adjustability | None | Orifice size can be changed in field | None without replacing snubber |
| Best for | Clean liquids and gases, laboratory instruments, steam service (with sintered SS) | Control loop transmitters where fast static response is required, pulsating pump/compressor service | General process gauge and transmitter protection, high-pressure service, sapphire orifice for abrasive service |
Pressure Snubber Selection: 5 Parameters to Specify
| Parameter | What to Specify | Tip |
|---|---|---|
| Snubber type | Porous, piston, or fixed orifice based on fluid cleanliness and response time requirement | Use piston type for transmitters on control loops. Use sintered for steam and clean liquid gauge installations. |
| Orifice or pore size | Liquid service: 0.3 to 0.5 mm. Gas and steam service: 0.5 to 0.8 mm. Viscous liquids: 0.6 to 0.8 mm. | Smaller orifice gives better damping but slower response and higher plugging risk. Match to the fluid viscosity. |
| Body material | 316 SS for most services. Monel for HF acid. Hastelloy C276 for strong acids and chlorides. Brass for non-corrosive utility services. | Match the snubber body material to the process connection and gauge wetted material. A 316 SS snubber on a Monel gauge defeats the corrosion protection. |
| Pressure rating | Snubber must be rated to at least the maximum process pressure including any pressure spike. Specify a safety factor of 1.5× the MAOP as the minimum snubber rating. | Water hammer spikes can reach 3 to 10 times the normal operating pressure in hydraulic systems. Use transient pressure calculations (Joukowski equation) for critical lines. |
| Connection size and type | 1/4 inch NPT or BSP is standard for most gauges. 1/2 inch for larger bore lines or higher flow. Match connection type (NPT vs BSP) to both the gauge and the process fitting. | A snubber with mismatched thread type (e.g. NPT snubber into a BSP gauge) will appear to make up but will leak. Always verify thread form before ordering. |
Orifice Pressure Snubber: Response Time Calculation
For a fixed orifice or piston snubber, the time constant of the gauge system can be estimated from the orifice flow resistance and the gauge cavity volume. This determines how quickly the gauge responds to a genuine step change in process pressure.
τ ≈ (8 × μ × L × V) / (π × r⁴ × ΔP_ref)
Where μ is dynamic viscosity (Pa·s), L is orifice length (m), V is gauge cavity volume (m³), r is orifice radius (m), and ΔP_ref is the reference pressure differential (Pa). This is derived from Hagen-Poiseuille flow through the orifice.
In engineering practice, snubber manufacturers publish response time in seconds per bar for each orifice diameter and fluid type. A 0.5 mm orifice in a typical 1/4 inch gauge body with water at 20°C gives a time constant of approximately 0.1 to 0.5 seconds, depending on gauge cavity volume.
Pressure Snubber Selection Checker
Pressure Snubber Installation Rules
Where a snubber is fitted matters as much as the snubber type. The following rules apply to all pressure snubber installations.
Vertical orientation for liquid service. Mount with the restriction at the bottom so trapped gas vents upward rather than blocking pressure transmission.
Install at the gauge, not at the tapping. Fitting at the tapping leaves the impulse line volume as capacitance, making the snubber largely ineffective. Always mount directly at the gauge connection.
Watch: Pressure Gauge Snubber and Accessories
Pressure Snubber Selection Questions
External References
- Pressure Snubber Types, Selection and Materials | Winters Instruments
- Snubber Selection Guide | Ashcroft (updated 2025)
What We Learn Today
- A pressure snubber protects gauges and transmitters from pressure spikes, pulsation, and water hammer by restricting the flow path to the sensing element.
- Porous snubber: best damping, no moving parts, prone to plugging in dirty service. Piston snubber: fast static response, preferred for control loop transmitters.
- Orifice size selection: 0.3 to 0.5 mm for clean liquids, 0.5 to 0.8 mm for gas and steam, 0.6 to 0.8 mm for viscous fluids.