Trafag EXPK 944/947/953 Ex Piston Pressostat

Flameproof piston pressure switch for high-pressure hazardous lines

The Trafag EXPK 944/947/953 is an electromechanical pressure switch with a piston sensor, built into an explosion-protected housing. It is certified to IECEx, ATEX and UKEX as II 2G Ex db eb IIC T6 Gb for gas and II 2D Ex tb IIIC T80 °C Db for dust.

The piston sensor covers ranges from 1 to 10 bar up to 60 to 600 bar, so it fills the gap above the bellows-type EXP pressostat on hydraulic, injection and high-pressure utility lines. The switch element is a microswitch with one floating change-over contact, and the housing is rated IP66 and can be mounted in any position.

Technical specifications of the EXPK 944/947/953

Standard types, differential and switch rating

Trafag lists four standard products with short lead time: the EXPK10 for 1 to 10 bar, the EXPK40 for 4 to 40 bar, the EXPK100 for 10 to 100 bar and the EXPK250 for 25 to 250 bar. Their overpressure ratings are 100, 200, 200 and 400 bar. The fixed switching differential grows with the range, from about 0.4 to 0.8 bar on the 10 bar sensor to 24 to 65 bar on the 600 bar sensor.

The standard Ex microswitch is rated 250 VAC at 5 A resistive and 0.25 A DC at 250 V, with 5 A at 30 VDC. Mechanical life is given as one million cycles, insulation resistance is above 2 megohm and dielectric strength is 1.5 kV.

EXP versus EXPK, wiring and installation

The bellows-based EXP covers low pressure and vacuum ranges, whereas the piston-based EXPK starts at 1 bar and reaches 600 bar. A piston sensor tolerates higher overpressure and suits pulsating pressure better, though the switching differential is larger. Where pressure peaks are likely, add a damping element or snubber; Trafag lists these in accessory datasheet H72258.

Connection is by screw terminals for conductors of 1 to 2.5 square millimetres through an M20x1.5 polyamide gland for cables of 4 to 13 mm. Replace the standard gland with an equivalent certified Ex entry if the plant standard requires it, follow the certificate conditions for the combined Ex db and Ex eb housing, and record the set point after commissioning.

Documents and quotation

The attached document is the Trafag EXPK 944/947/953 Ex pressostat datasheet (H72270u, 09/2024). Instructions and certificates are published separately by Trafag.

For a quotation, send the type (944, 947 or 953), range, connection, seal material and any stainless steel housing requirement. See Pressure Instrumentation for related instruments.