The main drains are usually located on the lowest point in the pool, so the entire pool surface slants toward them. Most of the dirt and debris that sinks exits the pool through these drains.
The main drain is located on the bottom of the pool in the deepest part. Most pools have one, but larger pools may have multiple main drains. Main drains must be protected by an approved cover. Water is also pulled into the pump through one or more skimmers, located on the waterline.
Main drains are not required in an inground swimming pool, however, they are strongly recommended and can be extremely useful in some circumstances. The advantages of main drains are to give you the ability to drain the water from your pool without the use of a sump pump. This is useful when replacing your pool liner.
So, if you see that you pressure quickly drops to 2 psi, it's likely that there's a leak in the main drain line somewhere between 4′ – 5′ under the water level of the pool. If there is a leak in the section of the line at or above the water level of the pool, you'll see a quick drop to 0 psi.
A pool's main drain can become clogged with debris. Your swimming pool's main drain requires regular maintenance. Although the rest of the pool's parts, such as the filter, may seem to be working just fine, the drain is always at risk of getting clogged.
Swimming pool builders often install overflow drains near the rim of the pool that prevent flooding most of the time. If you don't have an overflow drain, or if it is clogged, it is possible for periods of unusually heavy rain to overflow your pool.
Many pools do not have them. They are not required. They might add slightly improved circulation and can be helpful for removing debris, but there are ways to counter these without the floor drain.
A pool's so-called main drain is not actually a drain; that is, it is not used to drain the pool. Instead, it is an outlet, housing a pipe that runs to the pump, which sucks water through a skimmer, then through a filter, then through a heater (if you have one), and then back to the pool via multiple inlets.
Should the Pool Main Drain be Open? No, not if you are using a suction type of cleaner. The purpose of a pool main drain is to pull water from the bottom of the pool through the pump and filtration system.
A diverter valve is typically installed in the bottom of the skimmer box below the strainer basket. A pointer on one side of the valve indicates the setting. Rotating the valve so the pointer is directed toward the pool diverts all suction force away from the skimmer to the main drain.
Because the main drain is not tied into the skimmer in this set-up, pool systems using this configuration usually also have a separate valve to control a separate main drain line that runs from the pool to the pump.
Pool pumps usually have two pump drain plugs: one in the front, at the base of the hair and lint strainer or pump pot, and another plug further back toward the motor to drain the volute, or impeller housing.
When constructing a new swimming pool, if you are going to use a main drain it is required that you use two. This is due to safety regulations to help prevent Main Trap Entrapment. Main drain entrapment occurs when the suction is so great through a single main drain that a person can become stuck on or in the drain.
It may surprise those who've never had a pool, but typically in-ground swimming pools do not need to be drained. In the case of fiberglass pools you should NEVER drain your pool without first consulting your dealer. Even if the water seems beyond help, draining usually isn't the answer.
But large quantities of precipitation combined with an overflowing pool and poor drainage can cause problems such as flooding, structural damage to the surrounding buildings as well as out of balance swimming pool water chemistry. No fun.
Some pools have a hose spigot plumbed after the pump, or on the filter valve, which you can connect a garden hose, to lower water level. Or, you can use a submersible pump, aka pool cover pump, to keep the pool from overflowing. Finally, there is the siphon method. A pool vacuum hose works best.
The pool will only overflow by the amount of rain in excess of the amount of rain needed to fill the pool to the top. So if your pool is the normal 3” below the top, the rain would need to exceed 3” before any additional rain would be available to overflow onto the deck.
To find out which specific pipe is blocked, run your pool pump and check each line by itself by shutting off the other lines (skimmer lines, main drain line) and looking at your filter's pressure gauge. If a specific line has lower pressure than the other lines, then you've found your blockage.
During normal operation, water flows to the filtering system through two or more main drains at the bottom of the pool and multiple skimmer drains around the top of the pool. The main drains are usually located on the lowest point in the pool, so the entire pool surface slants toward them.
A skimmer is a necessary element of keeping a pool clean. The skimmer sits at the waterline and catches leaves, bugs and trash so they do not clog the filter. Skimmers with a second hole help keep the pump from running dry if the water level is unstable.
In order to tell if the valve is open or closed, the general rule is, if the handle is switched 90deg to the flow, it is off. As you can see from the diagram above, if the handle is in line with the flow path, it is on. Simple.