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Installation and Operation of the
DF Series Hydrostatic Head Level Switches
DF-94063N
Revised 09-03
Section 15
(00-02-0170)
Please read the following information before installing. A visual inspection of this product for damage during shipping is rec-
ommended before mounting. It is your responsibility to have a qualified person install this unit and make sure it conforms to NEC
and local codes.
GENERAL INFORMATION
WARNING
BEFORE BEGINNING INSTALLATION OF THIS MURPHY PRODUCT
✔ Disconnect all electrical power to the machine.
✔ Make sure the machine cannot operate during installation.
✔ Follow all safety warnings of the machine manufacturer.
✔ Read and follow all installation instructions.
*
**
CAUTION:
Certain dangers to human safety and to equip-
ment may occur if some equipment is stopped without
pre-warning. It is recommended that monitored functions
be limited to alarm only or to alarm before shutdown.
Description
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 body, nylon bottom plate and a special
alloy leaf snap-switch as standard.
This simple level switch is highly reliable and can be worked into most
new or existing system without major modification or special tools.
DF755 and DF757 are suitable for atmospheric tanks in a non-haz-
ardous location.
The SPDT snap-switch for the DF755 is preset for a 4 in. (102 mm)
differential in liquid level, operating at approx. 6 inches (152 mm) ris-
ing, and resetting at approx. 2 inches (51 mm) falling level.
The DF757 trip point is adjustable over a 108 inches (2743 mm) dif-
ferential.
Specifications
Snap-switch Ratings
SPDT (standard–all models)
• 5 A @ 125, 250, or 480 VAC
• 1/2 A @ 125 VDC, 1/4 A @ 250 VDC
Case/Lid: Aluminum (standard); 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.
Warranty
A limited warranty on materials and workmanship is given with this FW
Murphy product. A copy of the warranty may be viewed or printed by going
to www.fwmurphy.com/support/warranty.htm