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

DF-94063N page 3 of 4

The MAC1 Volume Air Cell when attached to the DF755 can monitor
water levels on a sump. Activate alarms or start a pump directly. The
MAC1 Volume Air Cell is non-corrosive and provides 1/4-20 stainless
steel mounting studs.

The MACT1 Tubing Kit provides 4 ft. (1.2 m) flexible, non-corrosive
1/4 in. (6 mm) tubing (cut to fit). The kit includes necessary fittings to
attach tubing.

Both the MAC1 air cell and MACT1 tubing kit are available from
Murphy.

Volume Cell Operation

As liquid rises around the volume cell, it compresses air inside the cell
and forces it up in the sensor line. As air pressure increases due to the
water level continuing to rise, sufficient pressure will be applied to acti­vate the internal snap-switch, which in turn starts the pump. As the liq­uid level is pumped down, pressure decreases and the above procedure
is reversed. The pump is stopped and held in a standby condition. An
air purge may be required in the sensor line. Consult factory.

Choosing a Volume Cell

The volume cell should be constructed of material which will be unaf­fected by the liquid being measured. For proper “pressure-to-level”
ratio, the minimum dimensions of the volume cell should be 6 in. (152
mm) inside diameter and 3 in. (76 mm) inside depth. The sensor line
can be of any diameter or material either flexible, or solid, as long as it
is of sufficient length to reach from the volume cell to the desired loca-

tion for the DF755. All fittings and connections should be air-tight to
avoid loss of “charge”. Tube lengths longer than 4 ft. (1.2 m) should
have provision for periodic air purging.

Installation of the Volume Cell

Install the volume cell according to the level you wish the pump to start
and stop. Secured the volume cell with a substantial bracket which will
not allow the cell to be “floated”
or tilted when the water level
rises. The DF755 should be
installed well above the highest
water level and in a position
that will allow access for
adjustment or repair.

NOTE: Periodically operate pump
manually until water level reaches a
point approximately 1/2 in. (13 mm)
below bottom of the volume cell. This
will automatically re-charge the unit
and compensate for normal
absorption of air into water.
Small electric air pumps are
available to automatically
charge system at all times.

USING THE DF755 WITH MAC1 VOLUME CELL ACCESSORY

AIR

Sensor Line
(MACT1 Tube Kit)

DF755

Volume Cell
(MAC1)

A

B

C

Hydrostatic Head
Pressure

Vent (DF755EX)
or Tube Fitting
(DF756)

B

C

A

Hydrostatic Head
Pressure

As the liquid level rises, hydrostatic head pressure is applied to the
diaphragm

A. The diaphragm is forced upward forcing the actuator arm B

to activate the snap-switch C.
Models DF755 and DF755EX are factory set and operate at approximately
2 in. (51 mm) and 6 in. (152 mm) rising above the level at which the
diaphragm is mounted. The switch resets back to normal condition at
approx. 2 inches (51 mm) falling level. The trip point(s) for Model DF757
are adjustable between 2 in. (51 mm) and 110 in. (2794 mm) for high and
low (make/break) operation by knobs,

D.

For sealed tanks, model DF755EX can be fitted with a tube fitting to bal­ance the top of the diaphragm chamber to a tank gas blanket (see Typical
Applications). The DF755EX is supplied with an atmospheric vent fitting.

Setpoint Adjustment (DF757)

1. Locate threaded adjustment shaft and adjustment

knobs (see drawing above).

2. To increase low level setpoint, rotate lower

knob counterclockwise.
NOTE: If adjustment shaft turns
when rotating adjustment knobs,
grasp the adjustment shaft with a
pair of needle nose pliers–then
rotate knob.

DF755

DF755EX

DF757

BASIC OPERATION

Adjustment
Shaft

C

B

D

A

Hydrostatic Head
Pressure

DF-94063N page 4 of 4

TYPICAL WIRING

SERVICE PARTS

Starts at Low Level, Stops at High

Start motor when predetermined low level is reached and stop when high
level is reached. Keeps tank level within selected limits. Motor starter
equipped with H.O.A.

Starts at High Level, Stops at Low

Start motor when predetermined high level is reached and stop when low level
is reached. Motor starter equipped with H.O.A.

Single Magneto Shutdown

Wiring of magneto to N.O. switch terminal will shut down engine at prede­termined high level, shown below. Wire to N.C. terminal to shutdown on
low level.

Dual Magneto Shutdown

Shutdown dual magneto engines using Murphy MS2120 Magnetic Switch.
Diagram below shows hookup for low level shutdown. Wiring changes and
mounting locations are necessary for high level shutdowns.

DF755

Description Part Number

Cover (aluminum) 15050081
Case (aluminum) 15050082
Cover Screws (3), #6–32 x 5/16 round head 80040607
SPDT snap-switch and movement assembly/repair kit (5 amp) 15000122
Screws (3) for switch assembly to case, #6–32 x 1/4 round head 80040605
Diaphragm repair kit 15000123
Bottom Plate (1 NPT connection) 15050083
Bracket and movement repair kit 15000313
SPDT snap-switch and insulator repair kit (5 amp) 15000121

DF755EX

Cover (aluminum) 15050154
Case (aluminum) 15050155
Gasket 15050305
SPDT snap-switch and movement assembly/repair kit (5 amp) 15000118
Screws (2) for switch assembly to case, #6–32 x 1/4 round head 80040605
Actuator assembly/repair kit 15000119
Diaphragm repair kit 15000123
Bottom Plate (1 NPT connection) 15050083
Screw (1), #8–32 x 1/4 round head 80040814
Terminal cup washer 00000827
Plug 1/8 plastic pipe hex (DF755EX) 86060203
Connector, 1/4 tube x 1/8 pipe male (DF756) 85030402
Plug 1/2 NPT hex (brass) 86060801
SPDT snap-switch and insulator repair kit (5 amp) 15000117

DF757

Cover (aluminum) 15050081
Case (aluminum) 15050594
Cover Screw (3), #6–32 x 5/16 round head 80040607
SPDT snap-switch and bracket assembly/repair kit (5 amp) 15000174
Screws (2) for switch bracket and assembly to case (#6–32 x 1/4 round head) 80040605
Spring and piston assembly/repair kit 15000190
Diaphragm repair kit 15000123
Bottom Plate (1 NPT connection) 15050083
SPDT snap-switch and insulator repair kit (5 amp) 15000230

MAGNETO

N.O.

C

N.C.

CONTROL SYSTEMS & SERVICES DIVISION

P.O. Box 1819; Rosenberg, Texas 77471; USA
[phone] fax [phone]

e-mail [e-mail]

MURPHY DE MEXICO, S.A. DE C.V.

Blvd. Antonio Rocha Cordero 300, Fracción del Aguaje
San Luis Potosí, S.L.P.; México 78384
[phone] fax [phone]
Villahermosa Office [phone]
e-mail [e-mail]
www.murphymex.com.mx

FRANK W. MURPHY, LTD.

Church Rd.; Laverstock, Salisbury SP1 1QZ; U.K.
[phone] fax [phone]
e-mail [e-mail]
www.fwmurphy.co.uk

MURPHY SWITCH OF CALIFORNIA

41343 12th Street West
Palmdale, California 93551-1442; USA
[phone] fax [phone]
e-mail [e-mail]
www.murphyswitch.com

In order to consistently bring you the highest quality, full featured products, we reserve the right to change our specifications and designs at any time.

MACQUARRIE CORPORATION

1620 Hume Highway
Campbellfield, Vic 3061; Australia
[phone] fax [phone]

e-mail [e-mail]

FW Murphy

P.O. Box 470248
Tulsa, Oklahoma 74147 USA
[phone]

fax [phone]
e-mail [e-mail]

www.fwmurphy.com

R

E

G

I

S

T

E

R

E

D

USA–ISO 9001:2000 FM 28221

UK–ISO 9001:2000 FM 29422

Printed in U.S.A.

C

C

HIGH

N.O.

N.C.

N.O.

N.C.

LOW

DF755

#1

DF755

#2

MOTOR

MOTOR

Magneto

Magneto

Model MS2120

6 2 3

1 4

Jumper #2 & #5

HIGH

N.O.

N.C.

N.O.

N.C.

LOW

DF755

#1

DF755

#2

N.O.

C

N.C.

C

C

5