Murphy DF User Manual

DF-94063N page 1 of 4

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 rec­ommended 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

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 equip­ment 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-haz­ardous 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) ris­ing, and resetting at approx. 2 inches (51 mm) falling level.

The DF757 trip point is adjustable over a 108 inches (2743 mm) dif­ferential.

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

WARNING

TYPICAL APPLICATIONS

DIMENSIONS

Typical Water Flood Control System

The diagram above displays eight DF Series switches installed on a
Raw Water tank and a Clear Water tank. When raw water rises to
predetermined level, DF#1 stops the supply pump. As tank level
falls below the predetermined level, DF#2 starts the supply pump. If
the tank level continues to fall, DF#3 initiates shutdown of the sup­ply pump. DF#4 stops transfer pump before raw water tank is com­pletely pumped out.
When clear water reaches the predetermined level, DF#5 stops the

transfer pump. As tank level falls to predetermined low level, DF#6
starts the transfer pump. If the tank level continues to fall due to the
failure of the filters section, DF#7 initiates shutdown of the transfer
pump. (DF755 located at this level will also operate backwash
equipment). DF#8 stops injection pump before tank pumps com­pletely out.
An OPL Series pressure SWICHGAGE

®

stops injection pump when

pressure reaches predetermined high or low pressure.

Tank with Low Pressure
Gas Blanket (DF755EX)

The DF755EX (below) is shown installed on a crude oil tank where
a low pressure gas blanket is used to prevent evaporation loss. It is
mounted directly to the side of the tank or on riser pipe 4 to 7 in.
(102 to 178 mm) below level to be controlled. Pump automatically
stops or starts when liquid reaches predetermined high or low level.

Typical Tank Mounting Methods (DF755)

Tank Wall Mounting With

Drain Cock

Bull Plug Installation

Directly
On Tank

Riser Pipe
Method

Tank Wall Mounting

DF755 and DF757

DF755EX

1 NPT
(standard)

6-5/32 in.
(156 mm)

5-1/2 in.

(140 mm)

1/2 NPT
For Electrical
Connection

7-21/32 in.

(194 mm)

5-5/8 in.

(143 mm)

1 NPT
(standard)

1/2 NPT
Plug

1/2 NPT
For Electrical
Connection

1/4 in. (6 mm)
Tube Fitting
(DF756 only)

DF-94063N page 2 of 4

Raw Water Tank Clear Water Tank

Supply

Pump

DF#1

DF#2

DF#3

DF#4

Transfer

Pump

Filter

DF#5

DF#6

DF#7

DF#8

Injection Pump

OPL Series

SWICHGAGE

®

Fuel Tank

Gas Blanket

Gas Liquid