Hydraulic Pressure Switches – 0.1 to 400 bar, Normally Open or Normally Closed

Two ranges of compact adjustable pressure switch on one page. The economy 48 volt range is the small 1/8″ BSPT male switch that fits almost anywhere, ordered as a normally open or a normally closed unit and adjusted with a flat blade screwdriver. The 250 volt AC range is a larger 1/4″ BSPP female switch with both contacts built in and a knurled knob you can turn by hand.

A pressure switch watches system pressure and, at the point you set it to, opens or closes an electrical contact – starting or stopping a pump, energising a solenoid, lighting a warning lamp, or dropping a machine out before something lets go.

Ways to buy:

• Off the shelf – choose your pressure range and model from the dropdown below.
• Need a G1/4″ BSPP male port and a change-over contact instead? See the F4 and K5 ranges linked below.
• Need a digital readout or a continuous signal? See the digital switches and transducers linked below.
• Protective caps and DIN plugs are listed separately – these switches are IP00 as supplied.

Economy range – up to 48V AC/DC, 1/8″ BSPT male

250V AC range – 1/4″ BSPP female

Specifications – economy 48V range

Specifications – 250V AC range

Piston or diaphragm?

Which sensing element you get is set by the pressure range, not by choice. Switches rated 50 bar and above use an internal piston. Switches rated below 50 bar use a diaphragm, which is more sensitive and gives a cleaner trip at low pressure. Both are inside the same body and neither needs anything different from you when you fit it.

Normally open or normally closed?

• Normally open – the contact is open with no pressure and closes when pressure reaches the set point. Use it to make something happen when pressure arrives: a lamp, a horn, an interlock that says the clamp is on.
• Normally closed – the contact is closed with no pressure and opens when pressure reaches the set point. Use it to stop something when pressure arrives, or as a low pressure alarm that trips when pressure falls away.
• Choose so that the safe state is the de-energised state. If a wire breaks or the switch fails, the machine should end up in the condition you would have chosen anyway.

How to choose

• Pick the range so your set point lands near the middle of it. A switch set hard against either end of its band is inaccurate and drifts.
• Check the port: the economy range is 1/8″ BSPT male, the 250V range is 1/4″ BSPP female. They are not interchangeable.
• Check the voltage and current your circuit needs. The economy switch is 48 V and 0.5 A – small. Anything bigger goes through a relay.
• Add a protective cap or DIN plug if the switch is anywhere it can get wet. These ship IP00, which means bare.

Technicians Advice

The number that catches people out on this range is the current rating: 0.5 amp at 48 volts on the economy switch is enough for a PLC input or a small relay coil and nothing else. Wire a contactor, a pump motor or a solenoid straight through it and the contacts will arc, pit and eventually weld closed – and a welded pressure switch reads as permanently “at pressure”, which is the failure mode most likely to hurt somebody.

Always drive a relay and let the relay carry the load. Fit the switch on a gauge port or a tee, never straight off the pump outlet, and put a snubber in front of it on any circuit that hammers. Remember these are supplied IP00 – the terminals are genuinely exposed – so on anything that gets washed down or rained on, budget for a protective cap or a DIN plug at the same time.

Set the trip point from the low side with the machine running and the oil warm, watch it on a gauge as it trips, then write the setting on a label next to the switch.

Complete your setup

Protective Caps and DIN Plugs

Need help choosing? Call 1300 146 737 or email sales@mhfgc.com.au – real technicians, real answers.