Call Us: (973) 256-3000 Plast-O-Matic Valves, Inc.
1384 Pompton Avenue
Cedar Grove, NJ 07009 USA

Series SWT Thermoplastic Pressure Switch

Corrosion-Resistant Design with No Wetted Metals or Elastomers

SWT Pressure Switch


  • Used to signal equipment when pressure in a piping system either rises or falls to a set pressure.
  • Adjusts easily with adjusting screw.
  • Maximum operating pressure of 150 psi via three easy-to-change spring ranges.
  • NEMA 4X design and patented Fail-Dry« enhance system safety.
  • Electrical switch is UL recognized and CSA approved.
  • Corrosion-resistant plastic cord grip and 18" cable simplify installation.
  • Better piston design and piston guidance vs. competition enhances reliability and accuracy.
  • Tested to 1,000,000 cycles in laboratory conditions.
  • PTFE diaphragm with no wetted metals or elastomers ideal for ultra-pure liquids.
  • Versatile snap-action 16 Amp/3 terminal switch is standard; 25 Amp and low deadband 3 Amp switches optional.

How it Works:

The Plast-O-Matic Series SWT Pressure Switch can be used to activate or de-activate equipment when pressure in a piping system either rises or falls to a set pressure. Liquid in the piping system acts against a Viton-backed PTFE diaphragm (the Viton does not contact liquid). The diaphragm works against a piston and spring, which triggers an electrical switch within the upper chamber of the unit. Spring pressure is set by simply threading the adjusting screw in or out.

Series SWT contains a snap-action electric switch with three terminals. One is common, one is normally-open, and one is normally-closed. The normally-open switch will close upon reaching the set pressure, and the normally-closed switch will open when set pressure is reached. Set pressure can be reached by higher system pressure falling to the set value, or when lower system pressure rises to the set value.

As an example, the switch can be set to actuate at 50 psi, rising pressure (switch actuates when pressure rises to 50 psi). When the pressure rises to 50 psi the normally-open contact will close, and the normally-closed contact will open. Therefore, depending on how the switch is wired, a light, or a pump, etc. can be energized or de-energized...or one item could be energized and another de-energized at the same moment. As the pressure continues to rise, no further changes occur....


If and when the pressure decreases, the switch will reverse, but not at 50 psi. Because of hysteresis (also known as "deadband"), the reversal will occur at approximately 40% lower pressure.

Deadband helps to prevent oscillation or "hunting." In other words, without sufficient deadband, the switch will be actuating and de-actuating too often. For applications where it is critical to de-actuate with less deadband, a 3-amp switch is available. See specifications below.

hysteresis or deadband of standard 16 amp and optional 3 amp switch

Chart above shows hysteresis or "deadband" as a percentage of set pressure. Shows where electrical switch will de-actuate under falling pressure, after actuating at set pressure.

Dimensions, Specifications & Ordering Information:

pressure switch  Dimensional Drawing

Part Number
Body Material
Pipe Size
Seal Material
1/2" NPT
1/2" NPT
1/2" NPT

Additional Specifications
Wetted PartsGeon« PVC, PTFE
Non-Wetted PartsPVC, Viton, Stainless Steel, Ethylene Propylene Rubber, nylon, Buna-nitrile.
Pressure RatingMax. 150 PSI @ 70║F
Operating Pressure3 Ranges: 15-50 PSI, 50-100 PSI, 100-150 PSI -- according to the spring installed. All three springs are included; the middle range (50-100) is installed by the factory unless otherwise specified.
Standard 16 Amp Switch Rating16 amps @ 125 VAC, 1/3 HP; 16 amps @250 VAC, 1/2 HP. UL Recognized and CSA Approved.
Optional 3 Amp Switch Rating3 amps @ 125 VAC and 250 VAC, UL Recognized and CSA Approved.
Optional 25 Amp Switch Rating25 amps @ 125 VAC, 1 HP; 25 amps @ 250 VAC, 2 HP. UL Recognized and CSA Approved.
Electrical Cable18" 3-wire stranded copper cable with .015 PVC jacket, indoor/outdoor, unshielded, 90║C, 600 volts

Installation Notes

The SWT can be mounted in any orientation. Performance may vary if the SWT is set in one orientation and changed to another; it should be set in the orientation in which it will be used.

The SWT has been laboratory tested to 1,000,000 cycles. Cycle life in field use may vary due to amperage, chemical attack, temperature and pressure variations, or other environmental factors. For example, using the switch at its maximum amperage rating may dramatically reduce the life of the electrical switch. The electrical switch is readily replaceable.

For detailed installation instructions, please click here.

CAD Drawing: SWT

Please click here to link to CAD file page with .DWG and 3D files

Catalog Page:

For specifications and catalog page in .PDF format, please click here.

Plast-O-Matic Valves, Inc. 1384 Pompton Avenue Cedar Grove,
NJ 07009 USA Phone: (973) 256-3000 Fax: (973) 256-4745
California Warehouse 4054 Brewster Way Riverside, CA 92501
USA phone: (951) 686-2852 Fax: (951) 686-6328
Email: Legacy home page: please click here