Pressure Switches for Piston Compressors
The pressure switch (pressostat) is an automatic switch that controls the electric motor of a piston compressor: it turns the motor on when pressure drops below the lower threshold and turns it off when the upper threshold is reached. The built-in thermal overload relay protects the motor from overheating, while the unloading valve releases pressure from the cylinder after shutdown — allowing easy restart.
Acvatron supplies Condor (Germany) pressure switches — the world leader in this segment — in stock at our Chisinau warehouse.
Pressure Switch Range
| Model | Specifications |
|---|---|
| Condor MDR3 10/10A | Pressure 4–10 bar, 10 A current, unloading valve, IP44, 230/400 V |
| Condor MDR3 16/16A | Pressure 4–16 bar, 16 A current, unloading valve, IP44, 230/400 V |
| Condor MDR2 10/10A | Pressure 4–10 bar, 10 A current, no thermal relay, budget series |
| Pressostat MDR41/11 | Pressure 1–10 bar, 16 A current, for small 220 V compressors |
How a Pressure Switch Works
The pressure switch connects to the compressor receiver via a G 3/8" threaded fitting. The internal diaphragm responds to pressure changes and closes or opens the motor power supply contacts. Thresholds are adjusted using two springs: main spring (∆P — differential) and secondary spring (Pmax — upper cut-out pressure).
Unloading valve (EV) — why it is needed
After the compressor stops, the valve automatically vents pressure from the cylinder head down to atmospheric level. This allows the motor to restart without load — start-up current drops 3–5 times, significantly extending the life of windings, start capacitors and relay contacts.
How to Choose a Pressure Switch
- Determine the maximum working pressure of your compressor (bar) — the pressure switch must be rated for it with a safety margin.
- Check the motor power supply type: 220 V single-phase or 380 V three-phase.
- Ensure the thermal relay rated current matches the motor current (shown on the compressor nameplate).
- Verify the receiver port thread: standard is G 3/8".
- Call an Acvatron engineer — we will select the correct model for your compressor brand free of charge.
Signs of a Faulty Pressure Switch
- Compressor does not start — switch fails to close contacts when pressure drops
- Compressor does not stop — switch fails to open contacts at Pmax
- Motor hums but does not start — contacts welded or unloading valve faulty
- Thermal protection trips frequently — thermal relay current too low or motor overheating
- Air leaking from under the switch — damaged diaphragm or faulty thread seal
Compatibility
- REMEZA AirCast: all СБ4/С and СБ4/C models (LB24A, LB30, LB40, LB50, LB75)
- MZB: V series (V-0.25/8, V-0.6/8), W series (W-0.36/8, W-0.9/8), FL series
- Fini, Abac, Fubag, Elitech, Калибр and any compressor with G 3/8" port
Pressure Switch Installation — Important Rules
⚠️ Installation and wiring of the pressure switch must be done only with power disconnected and receiver pressure at 0 bar.
- Bleed receiver pressure down to 0 bar before removing the old switch
- Seal the G 3/8" thread with PTFE tape or hemp + sealant
- Connect wires strictly according to the diagram: L1/N — 220 V supply, or L1/L2/L3 — for 380 V
- Check pressure settings before first start: factory default for MDR3 — 6–10 bar
