IOM-DA0
8
SECTION VIII
Figure 8:
Loading Pres sure Formula
LOADING PRESSURE FOR
MODEL
DA0
APPLIED PRESSURES
P
LOAD
= ISR Effect + Lower Piston Spring + Lower Piston Spring + Body Size
Compression Effect
Spring Preload Orientation Effect
P
Load
= P
2
+ [ISR x (P
1
– P
2
)] + C
V
Req'd
x
∆
P
Piston Spr.
+ LVPS + S/O
Factor
C
V
Max
ISR FACTOR
BODY SIZE
in (DN)
ISR – %
1/2" - 1" (15 - 25)
3.0
1 1/4" - 1 1/2" (32 - 40)
4.0
2" (50)
2.0
2 1/2" - 4" (65 - 100)
5.4
PISTON SPRING
LOWER PISTON
SPRING RANGE
psig (Barg)
∆
P Piston
Spring
psig (Barg)
LVPS
psig
(Barg)
none (none)
0 (0)
0 (0)
2 - 5 (.14 - .34)
3 (.21)
2 (.14)
1 - 2 (.07 - .14)
1 (.07)
1 (.07)
4 - 10 (.28 - 6.9)
6 (.41)
4 (.28)
SIZE / ORIENTATION – S/O
Factor
Body Size
in (DN)
Orientation
Cover Dome
on Top
Cover Dome
on Bottom
1/2" - 1" (15 - 25)
1
-1
1 1/4" - 1 1/2" (32 - 40)
2
-2
2" (50)
2.5
-2.5
2 1/2" - 3" (65 - 80)
3
-3
4" (100)
4
-4
VIII. PRESSURE LOADING
1. Loading pressure can be supplied using various
schemes. Please reference LOADING SYSTEMS
on web-site for the schematics of these various
schemes, including:
• pressure unloading using BPV
• pressure loading using PRV
• pressure loading using pilot
• pressure loading using I/P transducer
2. The Model DA0 exhibits a deviation in outlet
controlled pressure when the inlet pressure var-
ies; this “effect” is identified as ISR – Inverse
Sympathetic Ratio. Its relative pressure effect
can be calculated from the following equation.
