Gatevalve repair

READ THE DANGERS SECTION

The idea of this is so you get an idea of your system, so you know if your engineer is doing his job correctly, if you attempt a repair yourself,be carefull

This is a gatevalve. If yours doesnt look like this, try looking at Stopcock repair. The usual issues with gatevalves is either seized or leaking, be it internal or external. I will go through it top to bottom, skip the sections that dont apply to your situation.Most people will be looking at this because its seized or leaking. A gate valve works by forcing a wedge shaped chunk of brass down into a slot. If the system is full of debris (central heating etc), it will not close fully, so 'let by' when closed.

Ok, initialy, make sure the water is off and the system is drained, or your going to get wet. Open the valve all the way then close it one full turn. Holding the body of the valve with a wrench to prevent the pipework getting strained, unscrew the guts of the valve from the body. The body of a gate valve is quite short in relation to the thread size, so getting the valve open without straining the pipework can be difficult.

Now you have the guts of it out, have a quick look at the valve seats, (in this case its the angled sides of the chamber in the valve body) check for gubbins stuck in the bottom of the groove, pits on the faces etc. If it appears damaged, replace the entire valve.

The section you have removed now needs attention. Inspect the plug (bit that sits in the water) and its angled, machined, mating faces. They should be smooth with no signs of errosion or undue wear. Wind the plug off the spindle, check the internal and external threads for wear, and clean with cloth/tissue. Apply silicon grease to both thread sections, pushing it deep into the plug's thread. Put the plug back onto the the spindle, and wind it fully home, forcing the grease into all the crevices. Then open it again, clean it off, and grease it again. (the action of forcing new grease in will have shifted gunk from the very bottom of the plug thread)

Inspect the washer between guts and body, it should be good and free of cracks. Grease the thread and washer, screw the stopcock 'open' and screw back into the body, hand tight, making sure its seated all the way, now nip up tight. Note - this washer is hard to buy, so if damaged, replace with ptfe tape rolled into a thin 'sausage'.

If the stopcock leaks from gland nut, try nipping it tighter, just by little turns, trying the handle every time to make sure it still turns. If still leaking, remove the gland nut, and run a turn or two of ptfe round the shaft, where the 'cone' meets the valve. now retighten. This is the usual problem / reason why you are here, its usualy possible to do with the water on, without too much trouble.

Leaking washer between body/guts can be repaired LIVE, if you have a flood wish, and significant minerals. its best done by closing the valve, unwinding the guts 1/2 - 3/4 turn, nip the valve closed a little more, scrape out the old washer from the exposed gap and run ptfe around a couple of times. Open the valve a full turn (holding the insert in place) and tighten the body back down. BE AWARE, significant water may escape, the washer may be reluctant to leave, making the situation worse, the valve may pop apart, personaly, i think this is a bit too much for a DIYer

Valve Notes

• Gland nuts do leak. dont be afraid to nip them tighter
• If its tricky, consider fitting another valve further on in the system rather than fixing original
• Working on live water is the quickest way to a flood