Cashco 764PD User Manual
INSTALLATION, OPERATION & MAINTENANCE MANUAL (IOM)
IOM-764P / PD
MODEL 764P & 764PD
PNEUMATIC PRESSURE CONTROLLERS
SECTION I
I. DESCRIPTION AND SCOPE
The Model 764P is a pressure controller used for sensing static pressure, and outputting a pneumatic signal pro por -
tion al to the deviation from the setpoint.
The Model 764PD is a differential pressure controller used for sensing two static pressures (“HIGH” and “LOW”),
and outputting a pneumatic signal proportional to the deviation from the setpoint.
With proper materials selection, the units are suitable for gaseous, liquid or steam service. Refer to Tech ni cal Bulletin
764P-TB for design con di tions and selection rec om men da tions.
Use of oxygen gas as the IAS for a 764P or 764PD is outside the scope of this IOM, and is considered “special
construction”.
Abbreviations Utilized:
12-13
CCW – Counter Clockwise P1 – Inlet Pressure P/P – Pneu mat ic-to-Pneu mat ic
CW – Clockwise P2 – Outlet Pressure REV – Rev o lu tion or Re verse
DIR – Direct PB – Proportional Band SIG – Sig nal
EXH – Exhaust PC – Pressure Controller SRV – Safe ty Relief Valve
IAS – Instrument Air Supply PCV – Pres sure Control Valve TR – Con den sate Trap
PI – Pres sure Indicator V – Vent
SECTION II
II. INSTALLATION
1. A block valve of the globe/needle type should be
installed at the location of the pressure tapping.
Ball, butterfl y or gate valves are not rec om-
mend ed.
2. Recommended sensing tap pipe size is 1/2"
(DN15).
3. Location of pressure sensing tap should be in a
zone not subject to fl ow disturbances. Rec om-
mend a min i mum of 10 pipe diameters upstream
and 10 pipe diameters down stream from any
elbow, tee, valve, etc. that disturbs fl ow.
4. A pressure gauge is recommended at the location
of each tapping. Differential pressure designs
may in cor po rate a differential pressure gauge.
Supply @
P1
IAS @
60-100
psig
Airset
MODEL
764P
Port “A”
TR
EXH
Supply
Supply
PC
SIG
Port “B”
REV
“Output”
LOAD
PROCESS
DIR
P/P
V
PCV
Pigtail
Siphon
SRV
PI
Bypass
TR
Outlet
@ P2
5. A pigtail siphon is required for hot condensing
fl uids, such as steam, to assure a liquid trap at
the controller. The siphon should be installed as
near to the pressure connection(s) on the controller’s diaphragm hous ing as practical.
Blowdown - Drain
(Shaded portion for steam/condensate systems)
Blowdown - Drain
Figure 1: Recommended Piping Schematic for Pres sure
Reducing Control Valve with Positioner
6. It is recommended as a good practice to locate
the controller as close as practical to the pressure
tapping and at a similar elevation. For installations
where the controller was factory mounted on a
control valve unit, the pressure tapping should
be within 6 - 10 feet (2 - 3 meters) of the control
valve. (Remember to compensate for tappings
located above the elevation of the controller for
any liquid pressure head that may occur.)
7. The controller’s pneumatic output signal (SIG)
piping or tubing should be limited in length, and
con sid er ation must be given for the ultimate
pur pose of the SIG at its fi nal destination. The
fol low ing are recommended practices:
Purpose
SIG to Positioner
SIG to Supply Booster
LOAD to Actuator
1/4" O.D.
1/4" O.D.
1/4" O.D.
Tubing
Size Max Length*
100 ft.
100ft.
10 - 12 ft.
* Contact factory for longer lengths.
8. 764P controllers may be mounted by various
meth ods:
With Option -23; Field Bracket Mounting to Structure
Figure 3
Field Pipe Nipple Mounted. Recommend pipe tap
on top or side of pipe.
Bracket Mounted. Includes a bracket with
ma chine screws to allow attachment to a fi xed
struc tur al ap pend age; requires specifying Option
-23. (This is the method utilized when the 764P/
PD is spec i fi ed to be mounted to a control valve
ac tu a tor.)
Output Pipe Nipple Mounted to Model 2266 Control Valve
Figure 4
Figure 2
Factory Bracket Mounted to Ranger QCT Control Valve
2
Field Pipe Nipple Mounted to Piping
Figure 5
IOM-764P / PD
Panel Mounted. Not factory provided. Requires
fi eld provision of a panel opening and support
bracket per the below dimensions:
Panel
#10-32 machine
screws
PANEL CUTOUT
(Front View)
Countersink hole
for #10-32 fl at heat
machine screw.
Figure 6
Panel Mounted Assembly View
INSTALLED ASSEMBLY
(Bottom View)
#10-32 fl at head
machine screw and nut
Adjusting Screw
9. It is recommended that a 764PD be bracket or panel
mounted. A 764PD can be pipe nipple mounted
from 1/4" NPT connection.
10. Clean the piping and tubing of all foreign materials including chips, burrs, dirt, etc., prior to use.
Use care in applying thread sealant or TFE tape
to prevent excess material from entering the con nect ing pipe or tubing.
11. Controllers may be oriented in any position in doors.
Outdoors, recommended locations are with the
main lon gi tu di nal axis in a horizontal position, or
with the pneumatic sensor head directed down wards. Exhibit care to assure rainwater is pre vent ed
from entering the unused exhaust port (Port A or
Port B).
12. Connect piping/tubing per Tables 1 and 2.
13. 764P/PD’s can operate with a lubricated, nondried air supply. However, good practice and other
system com po nents (airsets, , relays, etc.) dictate
use of the highest quality air supply avail able.
If air can not be practically dried and bears oil,
coalescing fi lters should be utilized to remove as
much oil and water as possible, as well as particles
over 20 microns. Desiccant dried air is absolutely
required for outdoor installations ex posed to freezing temperatures.
14. For 764PD the system must be designed such that
the “HIGH” pressure is always at a higher value
than the “LOW” pressure is at the same time. If
the expected HIGH and LOW pressures reverse
with respect to each other, the unit will become
inoperative, and the output will increase towards full
IAS pressure of 18–20 psig (1.24–1.38 Barg).
TABLE 1
Controller
IAS to Port
A
B
Process
Pressures
Above Atm.
Pressure
Controller
IAS to Port
B
A
Vacuum
Process
Below Atm.
Pressure
NOTE: 764PD cannot be utilized in vacuum service.
Controller
IAS to Port
B *
A
B *
A
Direct
Supply
Exhaust
Increase in
pressure Increases
output signal
Increase in
differential pressure
Increases output
signal
Direct
Supply
Exhaust
Increase in
vacuum
Increases output
signal
TABLE 2
Pressure Reducing Applications
Control Valve Controller
ATO-FC
(REVERSE)
ATC-FO
(DIRECT)
Back Pressure/Relief Applications
ATC-FO
(DIRECT)
ATO-FC
(REVERSE)
* Common applications
764P
Action
Reverse
Exhaust
Supply
Increase in
pressure Decreases
output signal
764PD
Increase in
differential pressure
Decreases output
signal
764P
Action
Reverse
Exhaust
Supply
Increase in
vacuum
Decreases output
signal
Actions
ReverseIncrease in pressure
decreases output signal.
Valve "fails closed".
DirectIncrease in pressure
increases output signal.
Valve "fails open".
Actions
ReverseIncrease in pressure
decreases output signal.
Valve "fails open".
DirectIncrease in pressure
increases output signal.
Valve "fails closed".
Uncommon applications
IOM-764P / PD
3
SECTION III
III. PRINCIPLE OF OPERATION
1. The 764 controllers employ laminar fl ow to
pro duce the 3-15 psig (nominal 0.2–1.0 Barg)
output signal. Lam i nar flow eliminates the
need for range springs, levers, pivots and
other parts that pro duce friction and lost motion.
2. The sensing diaphragm in the 764P and 764PD
has a high spring rate and any change in the
sensed pressure produces a minute diaphragm
movement which strokes the sensor plate.
The sensor plate, in turn, throttles the fl ow
of in stru ment air through the sensor to develop the 3-15 psig (0.2-1.0 Barg) output signal.
3. On direct acting 764P controllers (see Figure 7) the
supply air enters PORT A and passes through the
pro por tion al band restriction. With an increase in
the con trolled pres sure the fl ow through the sen-
sor is reduced which in creas es the output signal.
The proportional band restriction regulates the
fl ow rate of supply air into PORT A. PORT B is
the ex haust port. A 764PD op er ates the same.
5. Closing (CW rotation) the proportional band ad just ing screw re duc es the proportional band. Open ing the screw in creas es the pro por tion al band.
6. The setpoint adjustment positions the sensor so
the diaphragm must defl ect its maximum for its
highest con trolled pres sure setting and hardly
de fl ects for the lowest con trolled pressure setting.
4. On reverse acting 764P controllers (see Figure
8) the supply enters PORT B (not PORT A). With
an increase in the controlled pressure, the supply
air fl ow ing through the sensor decreases, which
re duc es the output signal. The proportional band
restriction regulates the fl ow of exhaust through
PORT A. A 764PD operates in a similar manner.
OUTPUT SIGNAL
SUPPLY AIR
EXHAUST (VENT)
LOWER SENSED PRESSURE
HIGHER SENSED PRESSURE
4
IOM-764P / PD
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