Cashco DA4 - Manual (Page 12)

IOM-DA4 12
SECTION VIII
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 DA4 exhibits a deviation in outlet con-
trolled pressure when the inlet pressure var ies; this
“effect” is identifi ed as ISR – Inverse Sympathetic
Ratio. Its relative pressure effect can be calculated
from the following equation.
Figure 8: Loading Pres sure Formula
LOADING PRESSURE FOR
MODEL DA4
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