Cashco DA2 - Positive Differential - Manual (Page 3)

IOM-DA2 3
IV. PRINCIPLE OF OPERATION
1. Valve plug movements modulate the fl ow across
the valve seat to maintain the outlet pressure
(P
2
) equal to the sum of the differential pressure
(∆P
DIFF
) and the loading pressure (P
Load
). The
outlet pressure acting on the underside of the
diaphragm tends to close the valve plug against
the valve seat. The outlet pressure acting on the
topside of the diaphragm tends to lift the valve
plug off the valve seat. The positive differential
setting of the range spring tends to lift the valve
plug off the valve seat. The outlet pressure tracks
with changes to the loading pressure. Each one
psi increase or decrease in the loading pressure
produces a respective one psi increase or decrease
in the outlet pressure.
2. For a DA2 (single diaphragm) design, a com plete
diaphragm failure will cause the outlet process
fl uid to mix with the loading fl uid.
SECTION V
V. STARTUP
1. Start with the block valves closed.
2. Relax the range spring by turning the ad just ing
screw CCW for the DA2 (viewed from above) a
minimum of three (3) full rev o lu tions. This reduces
the ∆P
DIFF
(differential) pres sure set point.
3. If it is a “hot” piping system, and equipped with
a bypass valve, partially open the bypass valve
to pre heat the system piping and to allow slow
ex pan sion of the piping. Check for proper steam
trap operation if installed. Closely monitor outlet
(down stream) pressure via gauge to ensure not
over-pres sur iz ing. NOTE: If no bypass valve is
in stalled, extra caution should be used in starting
up a cold system; (i.e. do everything slowly).
4. Crack open the outlet (downstream) block
valve.
CAUTION C
Do not walk away and leave a bypassed reg u la tor
unattended!
5. Slowly open the inlet (upstream) block valve to
about 25% open, observing the outlet (down-
stream) pres sure gauge. Determine if the reg u la tor
is fl owing. If not, slowly rotate the DA2 regulator
ad just ing screw CW (viewed from above) until
fl ow begins. Slightly open the bleeder valve to
vent any air as the spring chamber is fi lling with
a liquid loading fl uid.
6. Continue to slowly open the inlet (upstream) block
valve until fully open.
7. Continue to slowly open the outlet (downstream)
block valve, especially when the downstream
piping system is not pressurized. If the outlet
(down stream) pressure exceeds the desired
pres sure, close the inlet block valve and go to
Step 2. Close bypass valve approximately 25%,
and re peat pro ce dure.
8. When fl ow is established steady enough that the
outlet (downstream) block valve is fully open, begin
to slowly close the bypass valve if installed.
9. Set the DA2 regulator set point (∆P
DIFF
) by turning
the ad just ing screw clockwise (CW) to increase
outlet pres sure or CCW to reduce outlet pres-
sure. The outlet (P
2
) pressure under these con-
ditions will approximate the desired dif fer en tial
pressure when loaded with P
Load
for the DA2.
10. Pressurize the source of loading (P
Load
) pres sure
and allow to fi ll the spring chamber cavity. Slightly
open the bleeder valve to vent any air as the
spring chamber is fi lling with a liquid loading fl uid.
11. Develop system fl ow and pressure and readjust
set point as required to obtain desired response.
Per for mance should be analyzed at minimum and
maximum fl ow levels.
12. Install closing cap where applicable. The standard
regulator relies on a double o-ring rotary seal (item
34) around the non-rising adjusting screw.
SECTION IV