SAFETY VALVE FLOATING

PROCEDURE FOR SAFETY VALVE FLOATING

1.0 OBJECTIVE

The objective of this procedure is to outline the general procedures involved in setting the safety valves to the designed set pressure before allowing the boiler to go for commercial operation. Follow the vendor’s manual for adjustment of set pressure.

2.0 PRE-REQUISITES
Ensure proper mounting of the safety valve exhaust pipe, such that no load is coming to the safety valves. Check the drip pan assembly and its drains are as per the requirements. Follow the instructions of the vendor for safety valve exhaust piping and its support.

3.0 PROCEDURE

3.1 Normally the highest set pressure valve is the valve floated first. While setting this valve other safety valve is gagged. Start the boiler as per cold start-up the procedure by modulating the firing. When the drum pressure reaches about 75% of operating pressure gently tighten gage on other safety valves. Raise pressure slowly by throttling the startup vent valve. When 80% of popping up pressure is reached manually operate the safety valve under test. This will blow off any debris or dust leftover in the valve internals.

Raise the boiler pressure by modulating the firing. When the pressure reaches nearer to the set pressure close the start-up vent. While the safety valve pops (lift), open the startup vent valve and note down the lifting /set pressure value.
When the valve sits back, note down the reset pressure. Control of drum level is important to avoid the possibility of water carryover from drum into the superheater.

The set pressure is adjusted by either tightening or loosening the adjusting nut. Tightening the nut increases the set pressure and vice versa. Blowdown which is the difference between set & reset pressure should normally be within 5% of the set pressure. For popping pressure and blowdown adjustment proceed as described below:

3.2 Popping pressure adjustment

Before proceeding to check the popping (lift) pressure, the accuracy of the pressure gauges to be used should be ascertained.
To adjust the popping pressure, remove the lifting gear, exposing the adjusting bolt lock nut. Loosen the lock nut if the opening pressure is low tightening (turn clockwise) the adjusting bolt if it is high loosen (turn counterclockwise) the bolt. When the desired pressure is reached –also after each adjustment –the lock nut should be securely tightened to prevent loosening of the bolt.

Caution: The adjusting bolt should never be turned when the boiler pressure is near the set pressure of the valve. Adjustments should be made when the boiler pressure is at least 10 % below the actual popping pressure of the valve. Unless this precaution is taken, the valve disc may rotate while against the nozzle and damage the seats.

3.3 Blowdown adjustment

When the popping (lift) pressure is changed a slight adjustment of the blowdown may be required. Raising the popping pressure lengthens the blowdown, lowering the popping pressure shortens.

Caution: Never make any ring adjustment when the boiler is under pressure without gagging the valve properly.

If the blowdown is not as desired when the set pressure has been obtained, it will be necessary to adjust the rings. The guide (adjusting) ring is the principal blowdown control ring. To change its position, remove the guide set screw on the back of the valve body. Insert a screwdriver or similar tool and engage one of the notches (these can be seen through set screw hole). The ring can then be turned to the right or left as desired. Turning the guide (upper) ring to the right raises it and reduces the blowdown. Turning the guide (upper) ring to the left lowers it and increases the blowdown.

After each adjustment always replaces and tightens the set screw being careful that its point engages a notch and does not rest on the top of the tooth.

Every safety valve is fitted with a lower or nozzle ring which permits very close adjustment when operating conditions make this desirable. This ring is carefully set before the valve leaves the factory and rarely needs adjustment as its main purpose is to do away with simmer or warn preceding the pop without much effect on the blowdown. No attempt should be made to eliminate short warn.

The nozzle ring is adjusted by removing the set screw and turning the ring with a screwdriver. Turning it counterclockwise to the right raises it and increases the popping power and thereby eliminates warn. The nozzle should be moved only one notch at a time and the valve action checked after each adjustment.

On a high-pressure valve, the nozzle ring can be very effective in reducing the blowdown. To reduce blow downturn the nozzle ring clockwise to the left (lower it) one notch at a time until the valve begins to warn or simmer before popping. When this notch is reached raise the ring one notch. Any further adjustment should be done with the guide (adjusting) ring.

Superheater safety valve should be set and adjusted on steam which is superheated near to the operating temperature. This is essential because the ring settings required for good operation with superheated steam are different from those for saturated steam.
The same procedure shall be followed for floating the other safety valves. While floating a safety valve other safety valves should be gagged.

Note: The boiler reaches the maximum design pressure during safety valve floating hence thermal expansion readings to be noted during this activity.

4.0 SAFETY

• The area around the safety valves and escape pipe should be barricaded and only essential personnel should be in the valve vicinity.
• Access platform to the safety valves as required should build with access and escape paths for emergency purposes.
• The high noise level during safety valve floating, therefore ear defenders must be worn by test team personnel.

PROTOCOL FOR SAFETY VALVE
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Checks prior to safety valve floating

1. Model and style of safety valve :
2. Type of gasket provided at inlet flange :
3. The tightness of flange bolts: Done
4. Exhaust piping & support status: Completed
5. Accessibility & working space near valve :
6. Gags for other safety valves
(Hand tightened only)
7. Hand Popping: Done

SAFETY VALVE FLOATING RESULT.

Valve tag No. SR. No Design Set (Lift) Press Actual Set (Lift) Press Reset Press Blow Down

Result: Accepted /Not accepted.