Curtiss-Wright 2600 Series Maintenance Manual Download Page 23

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Liquid Service

Liquid service valves must be set on water with set pressure indicated as
the first steady stream of water perpendicular to the outlet of the valve.
Intermittent opening and closing indicates leakage. The reduction in inlet
pressure required to reseat the valve depends on the rate of flow and
operator manipulation. Set the blow down ring to the position indicated in
Table 10.3. Do not attempt to adjust the blow down ring without gagging
the valve first (or reducing inlet pressure to zero). Remove the gag. When
the valve is first mounted there will be some air under the disc of the
valve. This may cause the valve to pop open suddenly. To remove the air,
lift up on the stem to let the air slowly seep out,
if possible. Pressure may need to be added
under the valve to assist in lifting the stem. Next,
raise the pressure to the desired set point. When
the pressure is within 90% of the set pressure,
raise the pressure at a rate of 1 psig per 2
seconds. Adjust the spring adjusting screw until
the desired set pressure is reached. We define
set pressure for a liquid valve as the first
continuous flow which is flowing 90 degrees
from the outlet. Confirm that you have the set
pressure correct by raising the pressure to
where the first steady stream is evident. Then,
lower the pressure until the valve re-seats.
Repeat this procedure until the valve shows a
consistent opening pressure.

Securing The Blowdown Ring

The adjusted position of the ring is maintained by a blow down ring lock
screw which threads into the valve body from the outside and engages
notches (like gear teeth) on the outside diameter of the blowdown ring.
To make an adjustment, loosen and remove the blow down ring lock screw
assembly. Insert a screw driver and rotate the nearest notch toward the
left to lower the ring or toward the right to raise it, counting the notches as
they are moved. Reinstall the lock screw assembly, ensuring that it
intercepts a notch without exerting side-pressure on the ring.

Seat Tightness Testing (Figure 10.1)

After the valve is satisfactorily checked for set pressure, it is necessary
to check the valve for seat leakage. It is important to minimize leakage
from pressure relief valves. Excessive leakage could lead to fouled and
inoperable valves, serious product loss and could also be hazardous to
personnel and equipment. The valve can be tested for tightness on the test
stand by increasing the pressure on the valve to 90 percent or more of the
set pressure and observing the discharge side of the valve for evidence of
leakage. Methods of determining leakage are covered by applicable
standards and specific user requirements.

API Standard 527 is a widely accepted standard for the procedure and
acceptance criteria for assessing the seat tightness of pressure relief
valves. The user should be familiar with this standard, in addition to any
information presented therein. The following seat tightness methods and
requirements are in general compliance with API Standard 527.

Air Testing

All openings from the secondary pressure zone shall be closed before
counting the bubble rate. This includes such items as caps, drain holes,
vents and outlets. A soap solution or equivalent test shall be applied to
secondary joints to detect escape of air other than that being measured.
Seat tightness tests are normally conducted with pressure at the pressure
relief valve inlet held at 90 percent of the set pressure immediately after
popping. For valves set at 50 psig or below, the pressure shall be held a 5
psig below the set pressure immediately after popping. Before starting the
bubble count, the test pressure shall be applied for a minimum of: 1
minute for valves of inlet sizes 2 inches and smaller; 2 minutes for sizes
2-1/2, 3, and 4 inches; 5 minutes for sizes 6 inches and larger.

Tube 5/16" (7.9 millimeters)

OD x 0.035 inch

(0.89 millimeter) Wall

Note: The cover plate should be

fitted with a suitable device to relieve

body pressure in case of accidental

popping of the valve.

1/2" (12.7 millimeters)

Water

Air Receiver

Figure 10.1

When making the adjust-