The DF series are diaphragm operated “hydrostatic head pressure” level switches. A pressure sensitive diaphragm operates a snap-switch that can be wired directly to electric pilot circuits to control pumps at predetermined levels. Typical application is to start and stop electric driven pump(s) to maintain tank levels. It is also applicable to engine driven pumps.

The nitrile sensing diaphragm is impervious to most liquids and is sensitive enough to control levels with 1/4 in. (6 mm.) repeatability. See model descriptions for limits of switch trip point adjustability. Materials include aluminum or optional bronze body for maximum corrosion resistance, nylon bottom plate and a special alloy leaf snap-switch as standard.

This simple level switch is highly reliable and can be worked into almost any new or existing system without major modification or special tools.

DF755 and DF757 are suitable for atmospheric tanks in a non-hazardous area. The SPDT snap-switch for the DF755 is preset for a 4 in. (102 mm.) differential in liquid level. The DF757 trip point is adjustable over a 108 in. (2743 mm.) differential.

DF755EX is the same as the DF755 except CSA listed for Class I, Division 1, Groups C and D hazardous areas.

Minimum trip point for all models is 1 in. (25 mm.) above the internal diaphragm.


• Water Flood Systems
• Crude Oil Tanks
• Salt Water Disposal Systems
• Diesel Day Tanks
• Sumps
• Cooling Towers




Snap-switch Ratings

SPDT (standard–all models)
• 5 A @ 125, 250, or 480 VAC
• 1/2 A @ 125 VDC, 1/4 A @ 250 VDC

SPDT (optional) †

• 15 A @ 125, 250 or 480 VAC
• 1/2 A @ 125 VDC, 1/4 A @ 250 VDC
• 1/8 HP @ 125 VAC, 1/4 HP @ 250 VAC

DPDT (optional) ††
• 10 A @ 28 VDCª
• 10 A @ 120, 230 VAC

Case/Lid: Aluminum (standard); Bronze (optional)–all non-explosion proof models
Bottom Plate: Glass-filled Nylon
Process Connection: 1 NPT (standard)
Maximum Pressure Rating: 25 psi (172 kPa [1.72 Bar])
Conduit Connection (electrical): 1/2 NPT

*CSA listing applies to DF755EX 20 in. (508 mm.) or less water column differential, 5A @ 125, 250, or 480 VAC.
**Products covered by this bulletin comply with EMC Council directive 89/336/EEC regarding electromagnetic compatibility except as noted.
† Not recommended for Sour Gas-H2S areas.
†† Not available on DF757 model.




A two-year limited warranty on materials and workmanship is given with this Murphy product. Details are available on request and are packed with each unit.