A rotary gate valve should be opened to the stop and then closed just a little. By leaving the valve just a bit closed, the stem packing is not compressed. This extends the life of the valve, and makes it easier to operate when it needs to be closed fully. A quarter-turn ball valve can be left fully open.
Ball valves may be the most reliable valve and are commonly used for main water shut offs. Similar to gate valves, ball valves should be all the way open to allow the full flow of water or all the way closed to restrict all water from flowing.
If a gate valve is partially open, the stem that holds and moves the gate will be in the water stream. If left in this condition for a long period of time, the water stream will wear away the stem, especially the end that attaches to the gate.
A gate valve is generally used to completely shut off fluid flow or, in the fully open position, provide full flow in a pipeline. Thus it is used either in the fully closed or fully open positions. A gate valve consists of a valve body, seat and disc, a spindle, gland, and a wheel for operating the valve.
When a gate valve is partially open, it closure element (disc or wedge) can vibrate against the seats and become scratched causing them to lose their seating integrity. The chief advantage of a gate valve is that it offers virtually no resistance to flow in the open position.
Open or closed: When the handle of a ball valve is parallel to the valve or pipe, it's open. When it's perpendicular, it's closed.
If you partially close a valve and you are flowing a relatively high amount of volume, upstream pressure may increase if it's not opening far enough to release pressure. If the valve is partially closed and you are flowing a relatively low amount of volume, it could release enough volume so that pressure decreases.
Your Home's Main Water Shut Off
Sometimes it can be found along a wall in your garage, or even under your kitchen sink. When turned off, it shuts down all water flowing into your home. As you can imagine, when a pipe bursts, knowing how to turn off that water flow becomes invaluable knowledge.
For a flowing system, closing an open valve half-way will reduce the flowrate, cause a higher pressure upstream of the valve, and a lower pressure after the valve.
Slowly turn level handle valves ¼ turn, until the handle is not parallel with the pipe. It should stop at a ¼ turn. Open a tub or sink faucet (hot and cold) on the highest level of the home to relieve pressure, and watch that spout to ensure that water has stopped flowing.
Turning the handle or stem too far with excessive pressure can cause damage and very often will cause a leak. Helpful tip: If you meet resistance when trying to open a main control valve, if it is a gate valve loosen the packing nut one turn. The packing nut is on top of the gate valve body.
After all faucets are open, let the COLD WATER run for at least 30 minutes. During this time, also flush each toilet in your home 2 or 3 times.
A quick and easy way to increase water pressure is to adjust the pressure-reducing valve, which can be found in your home, usually close to your water meter.
If your main water supply is turned off for any reason, it's best to shut down the water heater as a precaution until the supply resumes. Continuing to run your water heater when the tank isn't full could cause heat damage to the internal components.
If it does not fully stop water and you can shut off the flow prior to the valve, replace the stem washer. To repair a leak around the handle, replace the packing washer.
There may be a hidden plumbing leak in the walls of your home, or maybe your toilet is running when it's not in use. These “hidden” leaks can cause your home to be using water even when your main water valve is turned off.
Temperature changes – As the temperature increases in your plumbing system, water will expand and pressure will increase. This can occur as water is heated by the water heater, especially if it has a defective expansion tank or pressure relief valve.
During a valve closure, the kinetic energy of a flowing fluid is converted into potential energy in the form of pressure. This increase in pressure can be significant, potentially exceeding designed pipe pressure ratings.
pressure drop. As the valve is closed on a system in full flow, the resistance to the system flow that the valve provides (valve pressure drop) will increase by shifting from point A towards point B (See Figure 5b). This increasing resistance will use more of the head in the system, as well as decrease system flow.
The pressure differential between upstream and downstream where the valve opens is called the burst pressure. When the pressure differential exceeds the burst pressure, the valve piston “opens” and allows the fluid to flow.
To determine if a water valve is open or closed, there is a simple general rule you can usually follow. Basically, if the handle is turned 90 degrees to the flow, the valve is switched off.