Dwyer Instruments 1950 Operating Manual

Series 1950 Explosion-Proof Differential Pressure Switches

Specifications - Installation and Operating Instructions

et Point Adjustment

S

crew

S

/2˝ (12.7)

1

female NPT

Electrical

Conduit
onnection

C

Series 1950 Explosion-Proof Differential Pressure Switches com­bine the best features of the Series 1900 Pressure Switch with an inte­gral explosion-proof and weather-proof housing. Each unit is UL &
CSA listed; FM approved for use in Class I, Groups C & D; Class II,
Groups E, F, & G; and Class III atmospheres (NEMA 7 & 9). They are
totally rain-tight for outdoor installations. Twelve models allow set­points from .03 to 20 inches w.c. and from .5 to 50 psi (3.4 to 345 kPa).

Easy access to the SPDT switch for electrical hook-up is provided by
removing the top plate of the three-part aluminum housing. Adjustment
to the set point of the switch can be made without disassembling the
housing. The unit is very compact, about half the weight and bulk of
equivalent conventional explosion-proof switches.

CAUTION

For use only with air or compatible gases. Use of the Model 1950
switch with explosive media connected to the Low pressure port
(including differential pressure applications in such media) is not rec­ommended. Switch contact arcing can cause an explosion inside the
switch housing which, while contained, may render the switch inoper­ative. If switch is being used to sense a single positive pressure rela­tive to atmosphere, run a line from the low pressure port to a non-haz­ardous area free of combustible gases. This may increase response
time on -0 and -00 models.

Note: The last number-letter combination in the model number identi­fies the switch’s electrical rating (number) and diaphragm material (let­ter). The 2F combination is standard as described in the physical data
above. In case of special models, a number 1 rating is the same as 2;
a number 3 or 4 rating is 10A 125, 250, 480 VAC; 1/8 H.P. 125 VAC; 1/4
H.P. 250 VAC; a number 5 or 6 rating is 1A 125 VAC. Letter B indicates
a Buna-N diaphragm; N = Neoprene; S = Silicone; and V = Viton®.

Bulletin E-57

UL and CSA Listed, FM Approved For

L. I GR. C, D - CL. II GR. E, F, G - CL. III

C

Series 1950 Switches

Operating ranges and deadbands

pproximate

o order

T

pecify

s

odel Number

M

950-02-2S

1
1950-00-2F
1950-0-2F
1950-1-2F

950-5-2F

1

950-10-2F

1

950-20-2F

1

Model Number

1950P-2-2F
1950P-8-2F
1950P-15-2F
1950P-25-2F
1950P-50-2F

Operating
Range:

nches, W.C.

I

.03 to 0.10

0

.07 to 0.15

0

0.15 to 0.5

0.4 to 1.6

1.4 to 5.5

3.0 to 11.0
.0 to 20.0

4

perating

O

ange: PSI

R

0.5 to 2.0

1.5 to 8.0

3.0 to 15.0

4.0 to 25.0

5.0 to 50

1

t Min. Set Point

A

.025

0

0.04

0.10

0.15
.3

0

.4

0

.4

0

Min. Set Point

0.3 psi

1.0 psi
.9 psi

0

.7 psi

0

.0 psi

1

SPECIFICATIONS
Service: Air and non-combustible, compatible gases.
Wetted Materials: Consult factory.
Temperature Limits: -40 to 140°F (-40 to 60°C); 0 to 140°F

(-17.8 to 60°C) for 1950P-8, 15, 25, and 50. -30 to 130°F (-34.4 to

54.4°C) for 1950-02.

Pressure Limits:

Continuous: 1950’s - 45˝ w.c. (0.11 bar);
1950P’s - 35 psi (2.41 bar); 1950P-50 only - 70 psi (4.83 bar).
Surge: 1950’s - 10 psi (0.69 bar), 1950P’s - 50 psi (3.45 bar), 1950P-50
only - 90 psi (6.21 bar).

Enclosure Rating: IP54, NEMA 3, 7 and 9.
Switch Type: Single-pole double-throw (SPDT).
Electrical Rating: 15 A @, 125, 250, 480 VAC, 60 Hz. Resistive 1/8

HP @ 125 VAC, 1/4 HP @ 250 VAC, 60 Hz.
Electrical Connections: 3 screw type, common, normally open and
normally closed.

Process Connections: 1/8˝ female NPT.
Mounting Orientation: Diaphragm in vertical position. Consult factory

for other position orientations.

Set Point Adjustment: Screw type on top of housing.
Weight: 3.25 Ib (1.5 kg); 1950-02 model, 4.4 lb (2 kg).
Agency Approvals: CE, UL, CSA, FM.

RESPONSE TIME: Because of restrictive effect of flame arrestors,

switch response time may be as much as 10-25 seconds where applied
pressures are near set point.

A

ead Band

D

At Max. Set Point

.05

0

.05

0

.15

0

0.20

0.4

0.5

pproximate Dead Band

A

0.6

ax. Set Point

M

.3 psi

0

1.0 psi
.9 psi

0

.7 psi

0

.5 psi

1

DWYER INSTRUMENTS, INC.

Phone: [phone] www.dwyer-inst.com

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A. Fax: [phone] e-mail: [e-mail]

3-1/2

[88.9]

3/8

[9.53]

1-7/16

[36.5]

1/8 NPT(F)

PRESSURE

PORT

1-11/16

[42.9]

1/8 NPT(F)

HIGH PRESSURE

PORT

1/2 NPT(F)

ELEC.

CONDUIT

CONNECTION

RANGE ADJUSTMENT

SCREW

17/64 [6.75] DIA MTG

HOLES (2)

4-7/8

[123.8]

5-7/16

[138.1]

VENT DRAIN

PLUG

950 Switch Outline Dimensions

1

950-02: 7-3/4˝ (196.9) dia. x 4-11/32˝

1

110.3) depth. For complete dimensions

(

equest drawing 28-700175-00 from our

r
Customer Service Department

INSTALLATION

1. Select a location free from excess vibration and corrosive atmos­pheres where temperatures will be within the limits noted under
Specifications on reverse. Switch may be installed outdoors or in areas
where the hazard of explosion exists. See reverse for specific types of
hazardous service.

2. Mount standard switches with the diaphragm in a vertical plane and
with switch lettering and nameplate in an upright position. Some switch­es are position sensitive and may not reset properly unless they are
mounted with the diaphragm vertical.

3. Connect switch to source of pressure, vacuum or differential pressure.
Metal tubing with 1/4″ O.D. is recommended, but any tubing which will
not restrict the air flow can be used. Connect to the two 1/8″ female NPT
pressure ports as noted below:

4. To make electrical connections, remove the three hex head screws
from the cover and after loosening the fourth captive screw, swing the
cover aside. Electrical connections to the standard single pole, double
throw snap switch are provided by means of terminals marked “COM”
(common), “NO” (norm open), “NC” (norm closed). The normally open
contacts close and the normally closed contacts open when pressure
increases beyond the set point. Switch loads for standard models should
not exceed the maximum specified current rating of 15 amps resistive.
Switch capabilities decrease with an increase in ambient temperature,
load inductance, or cycling rate. Whenever an application involves one
or more of these factors, the user may find it desirable to limit the
switched current to 10 amps or less in the interest of prolonging switch
life.

A. Differential pressures - connect pipes or tubes from source
of greater pressure to high pressure port marked HIGH
PRESS, and from source of lower pressure to low pressure
port marked LOW PRESS.

B. Pressure only (above atmospheric pressure) - connect
tube from source of pressure to high pressure port. The low
pressure port is left open to atmosphere.

C. Vacuum only (below atmospheric pressure) - connect tube
from source of vacuum to low pressure port. The high
pressure port is left open to atmosphere.

ADJUSTMENT: To Change the Set point

1. Remove the plastic cap and turn the slotted Adjust-ment Screw at the
top of the housing clockwise to raise the set point pressure and counter­clockwise to lower the set point. After calibration, replace the plastic cap
and re-check the set point.

2. The recommended procedure for calibrating or checking calibration is
to use a “T” assembly with three rubber tubing leads, all as short as pos­sible and the entire assembly offering minimum flow restriction. Run one
lead to the pressure switch, another to a manometer of known accuracy
and appropriate range, and apply pressure through the third tube. Make
final approach to the set point very slowly. Note that manometer and
pressure switch will have different response times due to different inter­nal volumes, lengths of tubing, fluid drainage, etc. Be certain the switch
is checked in the position it will assume in use, i.e. with diaphragm in a
vertical plane and switch lettering and Dwyer nameplate in an upright
position.

3. For highly critical applications check the set point adjustment and if
necessary, reset it as noted in step A.

MAINTENANCE

The moving parts of these switches need no maintenance or lubrication.
The only adjustment is that of the set point. Care should be taken to keep
the switch reasonably clean. Periodically the vent drain plug should be
rotated, then returned to its original position. This will dislodge deposits
which could accumulate in applications where there is excessive con­densation within the switch. The Series 1950 Explosion-Proof Differential
Pressure Switch is not field serviceable and should be returned if repair
is needed (field repair should not be attempted and may void warranty).
Be sure to include a brief description of the problem plus any relevant
application notes. Contact customer service to receive a return goods
authorization number before shipping.

©Copyright 2012 Dwyer Instruments, Inc. Printed in U.S.A. 1/12 FR# 26-440332-00 Rev. 13

DWYER INSTRUMENTS, INC.

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A. Fax: [phone] e-mail: [e-mail]

Phone: [phone] www.dwyer-inst.com