- Connection: G1/2
- Material: stainless steel, Carbon steel (St 35.8)
- PN in bar: 63, 80, 100
- Temperature : 120, 300, 400 °C
- U-Form A, with connecting thread 1/2"
- U-Form B, with entry butt welding
 Datasheet
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- Connection: G1/2
- Material: Carbon-steel St 35.8, stainless steel
- PN in bar: 63, 80, 100
- Temperature: 120, 300, 400 °C
- Trumpet form , with connecting thread 1/2"
- Trumpet form with , entry butt welding
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Datasheet
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Gauge Siphons (Pigtails) – protection against over-temperature and pressure spikes
Gauge siphons—also called manometer siphons—protect pressure gauges and digital gauges in steam and hot-media service. A built-in condensate chamber forms a liquid barrier that significantly lowers the process temperature at the instrument and additionally damps pressure surges. Typical designs are U-type (straight) and ring/pigtail-type (coiled), with common connections such as G 1/2, G 1/4, 1/2" NPT.
Versions in carbon steel and stainless steel 304/316(L) cover a wide range of media and temperatures. On request, ICS Schneider Messtechnik supplies matching shut-off valves, snubbers/restrictors, gauge cocks, plus EN 10204 3.1 certificates and pre-assembled sets.
FAQ on Gauge Siphons
Answers on selecting the right design and material, installation, pressure/temperature limits, sealing concepts, and best practices for steam applications.
Which designs exist and when should I use them?
| Design | Key feature | Typical use |
|---|---|---|
| U-type (straight) | Compact, easy to clean | General service, limited space |
| Ring/Pigtail | Larger condensate volume, better damping | Hot steam, stronger pressure/temperature swings |
| Reinforced | Increased wall thickness | Higher pressures/harsh conditions |
Which material should I choose?
Carbon steel for saturated steam/standard duty; 316(L) for corrosive media/environments or higher temperature resistance. Select by medium, expected corrosion, and plant code.
What threads/connections are common?
| Process side | Instrument side | Standard |
|---|---|---|
| G 1/2, G 1/4 | G 1/2, G 1/4 | ISO 228 (BSPP, parallel) |
| 1/2" NPT | 1/2" NPT | ASME B1.20.1 (taper) |
| M20×1.5 (optional) | M20×1.5 | ISO metric |
How do I install a siphon correctly?
- Prefer a vertical orientation to ensure reliable condensate formation.
- Pre-fill with water/condensate before start-up (especially with hot steam).
- Provide a shut-off valve/gauge cock between siphon and instrument for service.
- Install threads strain-free and use the correct sealing method.
How does a siphon protect my gauge?
The condensate chamber lowers the temperature at the instrument; the loop acts as a mechanical restrictor against pressure spikes. This improves lifetime and reading stability.
What pressure and temperature ranges are feasible?
They depend on wall thickness, bore/size, material, and applicable code. For hot steam, stainless pigtails are often preferred. Observe project-specific limits (PED/ASME).
Which sealing concepts fit (BSPP vs. NPT)?
| Thread | Sealing | Note |
|---|---|---|
| G (BSPP) | Flat gasket/O-ring at sealing face | Keep faces flat and burr-free |
| NPT | PTFE tape or approved paste | Wrap in thread direction; tighten to spec |
Do I need to pre-fill the siphon?
Yes—especially for start-up temperatures > 100 °C, pre-fill with water so protection is effective from the first moment.
Which design damps better: U or pigtail?
Pigtail siphons usually provide greater damping and better thermal decoupling thanks to their longer tube path and larger condensate volume.
Can I add snubbers/restrictors?
Yes. Snubbers combined with siphons further reduce pulsation and cavitation, especially with rapidly changing pressures.
What typical issues should I watch for?
- No condensate → not pre-filled: risk of overheating the instrument.
- Thread leaks → wrong sealing concept or damaged faces.
- Sluggish indication → excessive damping (check snubber/medium).
How often should I maintain the siphon?
Include it in your regular plant inspections: visual check for corrosion/leaks, verify shut-off operation, clean/flush if fouled.
Can I combine a siphon with a diaphragm seal?
Yes. For critical media (viscous/corrosive), a diaphragm seal can be installed between siphon and gauge—consider weight and orientation.
Which documents/certificates can you provide?
On request: EN 10204 3.1 material certificate, factory test report, pressure/leak test, and project-specific tagging.
Are hygienic versions available?
For food/pharma, we recommend 316L stainless with suitable gaskets and low-dead-space installation; alternatively use hygienic process connections (Tri-Clamp/Varivent®).
What accessories are recommended?
- Gauge cock/shut-off valve for service/venting
- Snubber/restrictor for pulsation damping
- Adapters (G/NPT/metric) for standard changes
How do I size the siphon?
Base it on pressure, temperature, thread standard, and available space. For steam, a 1/2″ pigtail with an appropriate valve and matching G/NPT thread is common.
Tips for a long-lasting measuring point
- Mount the siphon without mechanical stress and support the piping.
- Apply external corrosion protection (coating/passivation).
- Re-tighten/check for leaks after thermal cycling.
Do you supply pre-assembled sets?
Yes—ready-to-install sets comprising siphon, shut-off valve/gauge cock, snubber, and gauge with documentation—matched to your thread standard and material.