Control Products N20 User Manual
SELECTING
DIFFERENTIAL PILOTS
NOTES ON SELECTION OF PILOTS
DIFFERENTIAL P
RESSURE REGULATOR PILOTS
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SELECTING DIFFERENTIAL PRESSURE PILOTS
SPENCE Differential Pressure Regulators may usually be classified in one or the other of the following groups:
1. Control of the delivery pressure at a constant, adjustable, predetermined differential above another source of fluid pressure.
This case is illustrated by the use of the SPENCE Type EN
Differential Pressure Regulator on a boiler feedwater make-up
line to control the delivery pressure of the feedwater at a constant differential above the boiler steam pressure. Another
example is the use of the Type EN to control the steam pres-
sure on a steam atomizing oil burner at a constant differential
above the oil pressure at the nozzle.
2. Control of the differential pressure or pressure drop across
the Pressure Regulator itself. This case is illustrated by the use
of the SPENCE Type EN24 Differential Pressure Regulator
installed in parallel with a heat exchanger to maintain a constant differential across it, thereby limiting the flow rate of
fluid through the heater.
The table below lists the principal Differential Pilots.
TYPE N AND N33 PILOTS require that the delivery pressure
(pressure of fluid discharged from the Regulator) be controlled
at a given differential above some separate source of loading
pressure.
TYPE N meets the requirements of most boiler feedwater
make-up and steam atomizing oil burner differential control
problems as described in the first group in the above table.
TYPE N33 is a version of the Type N in which two separated
diaphragms are employed to preclude the possibility of contact
between the two fluids applied to the pilot.
TYPE N20 is a differential relief pilot which causes the Main
Valve to open when its initial pressure exceeds the loading
pressure by a set differential.
Type Service Conditions Diaphragm Operating Main
Cast Iron Cast Bronze
a
Cast Steel
Differential
Characteristics Valve
Max. Max. Max. Max. Max. Max. Max. Max. Max.
Pressure
Normal Loading
Initial Temper- Diaph. Initial Temper- Diaph. Initial Temper- Diaph. Accuracy
Pressure ature Pressure Pressure ature Pressure Pressure ature Pressure Min. Max. Diameter Material
psi °F psi psi °F psi psi °F psi psi psi ± inches
N 250 450 240 300 500 290 600 750 300 3 150 1 psi 31/2 St. Stl. Spring
Closes on increase in differential E or C
Delivery pressure controlled at set Series
N33 250 450 240 300 500 290 600 750 300 3 150 1 psi 31/2 St. Stl. Spring
differential above loading pressure E or C
Loading Pressure may be any fluid Series
Opens on increase in differential
N20 250 366 250 300 366 300 300 366 300 3 150 1 psi 31/2 St. Stl. Spring
Initial pressure controlled at set E or C
differential above loading pressure Series
Loading pressure may be any fluid
a
Bronze Body Pilots are recommended for water service.
SIZING DIFFERENTIAL PRESSURE REGULATORS
DATA
REQUIRED FOR ORDERING
1. SERVICE Fluid flowing though Regulator.
2. INITIAL (INLET) PRESSURE
(a) Maximum/Minimum.
(b) Superheat, Gravity, etc.
(1) Steam Service–Total Temperature or Degrees
Superheat, if any.
(2) Air, Gases, Water and Liquids–Temperature and
Specific Gravity.
3. LOADING PRESSURE
(a) Maximum/Minimum.
(b) Fluid
4. CONTROLLED PRESSURE
(a) Maximum/Minimum.
(b) Fluid
5. DELIVERY PRESSURE Maximum/Minimum.
6. CAPACITY Maximum required flow through Regulator.
7.END CONNECTIONS Screwed or Flanged. (If flanged,
state drilling.)
SELECTION OF TYPE AND SIZE OF REGULATOR
MAIN VALVE
A. TYPE —See Selection Criteria
for Steam, Air, Gases or Water
and Liquids in beginning of this
Section.
B. SIZE—See applicable Valve
Capacity Tables in this Section.
C. MATERIAL— See Main Valve
Selection Chart in Technical
Reference Section or individual
Product Pages.
D. ACCESSORIES—See Accessories in Other Products
Section.
EXAMPLE
Select size and type Regulator to control the flow of water from
a Motor-Driven Centrifugal Boiler Feed Pump maintaining an
Excess or Differential pressure of 50 psi between the boiler
feedwater and the boiler steam pressure. The feedwater
temperature is 240°F. The boiler steam pressure is 150 psi.
Flow 90 gpm at 220 psi pump discharge pressure.
1. Water
2. (a) 220 psi
(b) 240°F
3. (a) 150 psi Boiler Pressure
(b) Steam
4. (a) 200 psi (Loading plus Excess Pressure)
(b) Water
5. Identical with Controlled Pressure, Item 4
6. 90 gpm
7. Flanged, if 2
1
/2" size or larger
SELECTION OF TYPE AND SIZE OF REGULATOR
MAIN VALVE
A. Since pressure drop across
valve (Initial Pressure minus
Delivery Pressure) is greater
than 10 psi:
SELECT TYPE E
B. For 90 gpm: SELECT 3"
C. For 220 psi, 240°F:
SELECT CAST IRON,
FLANGED 250 LB.
D. For Water Service:
Dashpot required.
PILOT
Since Initial Pressure 220 psi,
240°F, Differential (Excess)
Pressure 50 psi and the
Delivery and Controlled
Pressures are the same:
SELECT TYPE N
For 220 psi, 240°F:
SELECT BRONZE
None required in this case.
ANSWER: 3" SPENCE TYPE EN, CAST IRON BODY, 250 LB FLANGED ENDS,
EQUIPPED WITH BRONZE DASHPOT AND BRONZE PILOT BODY.
NOTE: Differential Regulators should always be protected by properly designed Strainers.
PILOT
See Selection Criteria
and Selection Charts
opposite.
See Pilot Selection
Chart opposite or individual Product Pages.
WATER CAPACITY TABLE–FLOW IN GALLONS PER MINUTE
These flow rates provide a simple method for sizing regulators or water pipes with inlet velocities in the
range of 240 to 600 fpm. Spence Regulators have variable seat sizes. The factory will select the proper
seat for particular flow and pressure drop. Additional capacity data is available on request.
VALVE OR PIPE SIZE
1
/4
3
/8
1
/2
3
/4 11
1
/4 11/2 22
1
/2 345681012
Velocity, fpm
247 251 255 262 270 277 285 300 315 330 360 390 420 480 540 600
1.3 2.5 4.0 7.3 12 22 30 52 78 127 238 405 630 1250 2210 3490
Velocity, fpm
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SIZING DIFFERENTIAL
REGULATORS
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