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Pepperl+Fuchs Blog

Class I Applications for Type Y and Type Z Purge Systems

Posted by Brent Dean on Fri, Mar 01, 2013

Differences between the WPS and WPSA pressure switches

When selecting a Type Y or Type Z purge system, how do you know when to select the WPS (EPSK-1) or WPSA (EPSK-1A) pressure switch, and what is the difference? When selecting which pressure switch to use, first you must determine what hazardous gas group your enclosure is going to be located in (Group A, B, C, D, etc.).

The WPS pressure switch is rated for Class I Division 1 or 2 gas groups C and D. The WPSA switch is rated for Class I Division 1 or 2 gas groups A-D. For gas group C or D, you can use either switch. However, for gas group A or B, you must use the WPSA switch because it is certified for this area.

Select a pressure switch for a purge system

(EPSK-1 represents the WPS switch and the EPSK-1A represents the WPSA switch)

Now that you know which switch you want to use based on the location of the hazardous area, let’s go over the differences between the switches.

The WPS switch is just a dry set of contacts. When the pressure drops below the set point, the contacts close. A diaphragm in the switch senses the pressure and can set off an audible/visual alarm or send a signal back to your control system informing that pressure was lost.

The WPSA switch can also set off an audible/visual alarm or send a signal back to your control system if pressure is lost. Unlike the WPS switch, the WPSA switch is an electronic pressure switch. (See wiring diagrams below.)Wiring diagrams for pressure switches

(Here you must provide separate power to the WPSA pressure switch with a default 120 VAC power supply but 240 VAC and 24 VDC options are also available)

Please note that for ATEX applications with our 3003 and 3004 purge units, you must use either the LPS model (without a pressure switch or “Less Pressure Switch”) or the WPSA switch. The WPS switch is not certified for ATEX applications.

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Topics: Purge/ Pressurization Systems, Ask an Expert, Approvals/ Certifications

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