A gate valve for a property usually has to be closed if plumbing repairs or maintenance are needed inside the building. In some instances, particularly if the main control valve is a gate type valve, the valve may not close completely. This is typically due to sediment that has built up inside the body of the valve which becomes lodged between the gate that lowers and the valve body itself. Ball type valves do not suffer from this problem as they operate on a different principal than a gate that raises and lowers inside of the valve body.
The typical reaction when a gate valve will not close fully is to exert addition force on the handle. This is absolutely the wrong response and can cause permanent damage to the valve and a loss of water supply to the building. If sediment or mineral deposits are preventing the gate valve from closing fully there is a more sensible first step to take.
The first step if a gate valve will not close completely
If sediment or mineral deposits are preventing a gate from closing completely an attempt should be made to flush out the inside of the valve. The proper way to do this is to open a faucet on a sink inside the house so there is a flow of water. Then gently and repeatedly open and close the valve. If the handle of the valve does not turn freely then loosen the packing nut just above the valve body and around the stem of the valve. Loosening it just one turn should be fine – just remember to tighten it back up when you are done. Every time you lower the gate some sediment will break free and be flushed away by the water flow. There is absolutely no harm or danger in how many times you do this as long as no excessive force is used. In fact, routinely opening and closing a gate valve helps it to last longer than if it is left frozen in place for long periods of time. This is called exercising the valve.
What if the valve stops almost all of the water flow?
Sometimes a little water will continue to flow after a gate valve is closed as fully as possible. In some cases the plumbing repairs inside the property can be performed with a little bit of water flowing through the system. But there is an other option as well. If there is a slight flow of water the easiest solution is to jump the valve. That simply means to leave the defective valve in place and simply install a brand new valve after it. If legal for your area and for your type of water service line the preferred valve to use is a ball type valve. A full port ball valve allows for full flow of water, is rated higher than most gate valves, is longer lasting, and is not prone to break.
If you choose to install a second main control valve it is a good idea to remove the handle on the original valve or label it as a reminder so it is not used in the future. The last thing you would want to do is use the old defective valve in the future and have it break in the closed position.
What if a gate valve breaks in the closed position?
In most cases if a gate valves breaks in the closed position extensive work has to be done. Sometimes a curb valve will be located in the sidewalk area which would enable you to close the curb valve using the proper tool. You could then remove the broken valve with little trouble. If there is very little room to work inside the basement where the valve is located and there is no curb valve, the roadway may have to be opened in order to close the tap connection itself. Opening the roadway can be fairly costly and will involve securing DOT permits.
Changing out a main control valve under pressure can be a very tricky proposition and sometimes dangerous. Removing a valve under water pressure can sometimes be done by highly skilled plumbers, but never when live electric services are nearby. One should never risk an injury just to save a few dollars.
There is a trick of the trade that can be shared. If a gate breaks in the closed position there is a way to raise it back up to restore water service. By drilling a small hole near the bottom of the valve body in line with the gate a nail or some other sharp object can be pushed in to force up the gate of the valve. Water will leak out while this is being done but it will be a manageable amount. After the valve gate is pushed up simply insert a like-sized sheet metal screw into the hole to stop the water. Please note that while this will restore the water supply to the building it is a temporary fix. The gate valve will still have to be replaced to make a permanent repair and have a trustworthy valve to close the water in the future.
As in most cases it is strongly suggested that a Licensed Master Plumber be contacted when a plumbing repair is required.