IOM-DA8
3
IV. PRINCIPLE OF OPERATION
1. Valve plug movements modulate the flow across
the valve seat to maintain the inlet pressure (P
1
)
equal to the sum of the differential pressure (
∆
P
DIFF
)
and the loading pressure (P
Load
). The inlet pressure
acting on the underside of the diaphragm tends to
lift the valve plug off the valve seat. The loading
pressure acting on the topside of the diaphragm
tends to close the valve plug against the valve
seat. The positive differential setting of the range
spring for the DA8 tends to close the valve plug
against the valve seat.
2. For a DA8 (single diaphragm) design, a com plete
diaphragm failure will cause the inlet process fluid
to mix with the loading fluid.
SECTION V
V. STARTUP
1. Start with the block valves closed.
2. Relax the range spring by turning the ad just ing
screw CCW (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 inlet
(up 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
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 inlet (up stream)
pres sure gauge. Determine if the reg u la tor is
flowing. If not, slowly rotate regulator ad just ing
screw CCW (viewed from above) until flow begins.
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 pip-
ing system is not pressurized. If the inlet (up 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 flow is established steady enough that the
outlet (downstream) block valve is fully open, begin
to slowly close the bypass valve if installed.
9.
Under normal operating conditions, set the
DA8 regulator set point (
∆
P
DIFF
) by turn-
ing the ad just ing screw clockwise (CW) to
increase inlet pres sure or CCW to reduce
inlet pressure. The inlet (P
1
) pressure un-
der these conditions will approximate the
desired dif fer en tial pressure for the DA8.
10. Pressurize the source of loading (P
Load
) pres sure
and allow to fill the spring chamber cavity. Slightly
open the bleeder valve (item 3) to vent any air as the
spring chamber is filling with a liquid loading fluid.
11. Develop system flow and pressure and readjust
set point as required to obtain desired response.
Per for mance should be checked at minimum and
maximum flow 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
