Gate Valve Troubleshooting

1. LEAKAGE
2. VALVE IS HARD TO OPERATE OR IS INOPERABLE
3. VALVE LEAKS DURING TESTING

PROBLEM

LEAKAGE

SOLUTION

Depending on the location of the leakage, the following should be examined.

1. SEAT: Foreign material may be stuck under the valve wedge. Open valve only enough to get high velocity flow to flush out valve. Repeat several times until leak stops. If this does not solve the problem it is then necessary to open the valve and check for damage to the rubber encapsulated wedge. If it is damaged or severely cut, replace the wedge.

2. STEM: The stem seals are of the O-Ring type, and the valve has a stem collar (electrically actuated valves normally do not have stem collars). The seals can be replaced while the valve is under water pressure by back seating the valve in the open position. On OS&Y valves leakage can be stopped by evenly tightening the packing gland bolts. If leakage cannot be stopped, the valve should be repacked.

3. BODY: Check for cracked or damaged valve body or bonnet. If damage has occurred, contact manufacturer for further instructions.

4. BOLTED CONNECTIONS: Check for loose bonnet-to-body bolts, seal plate bolts or end joint bolts and tighten as necessary. This should be done prior to pressurization of the line. If line is pressurized, pressure should be relieved prior to tightening any bolts. Do not tighten bolts past the yield strength of the bolt. Reinstall all bolts and nuts and tighten alternately to 70-90 ft.-lbs. of torque.

PROBLEM

VALVE IS HARD TO OPERATE OR IS INOPERABLE

SOLUTION

1. A valve can become inoperable or hard to operate during testing of the pipeline. Prior to relieving pipeline pressure, the valve should be opened to relieve any trapped pressure.

2. Over-torquing a valve can cause permanent damage to the operating parts. A primary cause for over-torquing comes from a portable actuator. Output torques generated by these machines should be adjusted to be suitable for the valve size. The last or first turns of operation should be done by hand.

VALVE SIZE	2"	2-1/2"	3"	4"	6"	8"	10"
Number of turns to open/close	9	9	10	13	19	26	32

VALVE SIZE	12"	16"	18"	20"	24"	30"	36"
Number of turns to open/close	38	50	56	62	73	*	*

*Contact American Flow Control for number of turns.

3. If valve has not been operated periodically, excessive buildup could occur that would affect valve operation. The valve should be exercised one turn at a time and cycled from open to closed as necessary to attempt removal of internal buildup.

PROBLEM

VALVE LEAKS DURING TESTING

SOLUTION

1. Resilient seated gate valves per AWWA C515 have a zero allowable leakage rate. If a leak is detected while testing, it is necessary to find the cause.

2. If seat leakage is detected, it may be due to trapped air or foreign material in the line. Open the valve enough to get high velocity flow to flush out valve. Repeat several times until leakage stops.

3. If testing between valves, allow enough time to fill the valve and vent off air.