How to Adjust Pool Skimmer Suction Safely

Locating Your Suction Controls: Pad Valves vs. In-Skimmer Diverters

Before you turn any handle or move any plastic plate, you need to know where your pool regulates water flow. Pool water moves through pipes because the circulation pump pulls water from the pool, pushes it through the filter, and sends it back through the return jets. That pulling force enters the system through two main places: the skimmer boxes at the surface of the water and the main drain grates at the deepest point of the pool floor. Where you control that balance depends on how the builder set up your plumbing.

Most modern in-ground pools control this balance at the equipment pad, where the pump and filter sit. In front of the pump, you will find an intake pipe rising out of the ground with a three-way valve (a handle on the pipe that splits flow between two lines). This valve connects the line coming from your skimmer to the line coming from your main drain. Turning the handle shifts water intake toward one pipe or the other, letting you give the skimmer more pulling power or share that power evenly with the bottom drain.

Other pools, including many older in-ground installations and specific above-ground pools, do not have separate valves sitting by the pump. Instead, both the skimmer line and the main drain line tie together beneath the pool deck, and the control sits right inside the skimmer box beneath the removable basket. When you take out the basket, you will see two open ports at the bottom. Suction here is controlled by a diverter plate (a movable plastic saucer covering the hole inside the skimmer) or a floating valve dome that covers the openings. Sliding or rotating this piece changes how much suction reaches the skimmer opening versus the bottom drain.

Single-port skimmers are common on above-ground setups. In these pools, a single hose runs straight from the skimmer box to the pump intake. Adjustments on these pools do not split flow with a floor drain. Instead, you balance suction using an inline shutoff valve placed directly on the hose, or by adjusting a bypass disc attached to your vacuum plate inside the skimmer.

Step-by-Step Guide to Adjusting Suction at the Equipment Pad

Adjusting flow at the equipment pad gives you the most direct control over your skimmer. The goal is to give the skimmer enough power to clear leaves and dust without starving the pump of water. Follow these steps in order to balance your suction safely.

1. Inspect water level and clean all strainer baskets.

   Check that the pool water level sits halfway up the skimmer mouth. Empty the skimmer basket and the pump strainer basket before adjusting anything.

   Reason: Packed baskets and low water choke off flow on their own. Clearing debris first ensures you are adjusting actual plumbing pull rather than reacting to a temporary clog.

2. Identify the skimmer and main drain pipes.

   Trace the pipes entering the front intake port of your pool pump. If your pipes lack labels, note that the pipe coming from the skimmer usually enters straight from the direction of the pool deck, while the main drain line often runs alongside it from the deep end.

   Reason: Knowing which pipe leads where prevents you from accidentally turning off the skimmer completely when your goal was to increase its power.

3. Loosen the center locking knob on the valve handle.

   Find the round thumb knob sitting on top of the valve handle and turn it two full turns counterclockwise. Do not unscrew it completely.

   Reason: The locking knob clamps the handle against internal teeth. Loosening it lets the handle turn smoothly without cracking the plastic casing or stripping the stop tabs.

4. Nudge the handle in tiny quarter-inch increments toward the main drain pipe.

   Most three-way valve handles have an indicator tab or a label that says "OFF." Whichever pipe that "OFF" tab points toward is the pipe being restricted. To increase skimmer pull, move the "OFF" tab slightly toward the main drain pipe to reduce drain flow and route more suction to the surface skimmer.

   Reason: Making tiny turns lets the water pressure equalize gradually and prevents sudden air pockets from entering the plumbing.

5. Check the clear pump lid for air bubbles.

   Look directly through the clear glass or plastic lid on the pump basket. The water beneath the lid should remain solid, clear, and quiet. If you see violent churn, foaming, or a growing air pocket, you turned the valve too far and are choking off the water supply.

   Reason: The pump needs a continuous rush of water to keep its motor cool. Starving the intake causes cavitation (the pump choking on air and running dry), which damages internal seals within minutes.

6. Confirm surface skimming movement at the pool edge.

   Walk over to the skimmer box and watch the weir door (the hinged flap swinging in the skimmer mouth). The flap should bob gently, drawing surface film and floating leaves into the basket without creating a loud sucking vortex.

   Reason: Visual confirmation at the water line proves that surface velocity is strong enough to capture debris without pulling in air funnels.

7. Hand-tighten the center locking knob.

   Once surface movement looks steady and the pump pot runs clear of air bubbles, tighten the center knob clockwise until it is snug. Avoid using wrenches or pliers.

   Reason: Pump vibration during daily filtration cycles can slowly shift loose valve handles out of position over time.

Adjusting Suction Inside the Skimmer Basket

If your equipment pad does not have a valve on the intake pipe, your flow adjustment happens directly inside the skimmer well. Remove the skimmer lid on your pool deck and lift out the plastic basket to expose the bottom of the well.

In a two-hole skimmer, the port closest to the pool wall outer edge usually leads to the pump, while the port closer to the pool interior leads to the main drain. If both holes are wide open, the pump takes the path of least resistance, which often means pulling heavily from the main drain while surface pull remains weak. To fix this, pool builders use a diverter plate (a movable plastic saucer covering the hole inside the skimmer). This saucer features a rotating flap or sliding notch on its underside.

Place the diverter saucer over both holes at the bottom of the skimmer well. To increase skimmer suction, rotate the underside flap so it partially covers the main drain hole while leaving the pump hole open to the skimmer well. This forces the pump to draw more water directly through the skimmer basket from the pool surface. If the skimmer begins pulling so hard that it sucks in air, turn the saucer flap so it opens more of the main drain hole, which relieves surface suction by drawing more water from the floor.

Some pools use a float valve assembly, which looks like a plastic cylinder or dome with a swinging gate underneath and an O-ring seal around the rim. The float valve sits directly over the twin ports. If water inside the skimmer drops suddenly, the internal float drops down, shutting off the skimmer port and opening the main drain port completely so the pump never runs dry. You can adjust the trimmer plate on the underside of this float valve by hand, opening or closing the small slit to fine-tune how much water draws from the pool surface during regular operation.

For single-port pools, like many soft-sided or metal-frame above-ground setups, you do not have a second hole to balance against. If your surface suction is too violent or pulling the skimmer down, you can install an adjustable bypass plate over the skimmer mouth or an inline ball valve along the flexible hose. When maintaining these setups, being gentle with the plastic wall fittings is essential. If you want to keep the surrounding pool structure in prime shape, learning how to clean an Intex pool without damaging the liner helps prevent excess strain on the wall cutouts around your skimmer.

Warning Signs That Suction Is Set Too High or Too Low

Setting your skimmer flow requires finding the sweet spot where debris vanishes quickly without straining your plumbing. Watch for these clear signs to know if your suction balance needs a reset.

Signs suction is set too high:

• A spinning whirlpool or vortex forms inside the skimmer well, making a loud, rhythmic slurping sound as it pulls air straight into the pipes.
• The weir door (the hinged flap swinging in the skimmer mouth) gets sucked down flat against the bottom of the opening and cannot bob freely.
• Large air bubbles shoot out of the return jets across the pool, clouding the water with fine white mist.
• The clear pump pot at your equipment pad fills with swirling air or white foam, signaling cavitation (the pump choking on air and running dry).
• The pump motor sounds louder than usual, producing a harsh, gravelly grinding noise instead of a smooth, low hum.
• A suction-side vacuum cleaner clings aggressively to the pool floor, struggling to move or flattening its rubber seal against the surface.

Signs suction is set too low:

• Pollen, pine needles, and bugs drift right past the mouth of the skimmer without being pulled inside.
• The weir door hangs motionless in the water instead of gently pulsing with the flow.
• A floating film of sunblock oils collects around the pool waterline because surface water stays still.
• A suction cleaner hooked to the skimmer moves at a crawl, fails to climb walls, or stops working altogether.
• Water flow through your heater drops below safe operating limits. If water circulation slows down too much, internal pressure switches cut off operation, which is a key checkpoint when you prepare to safely turn on a Hayward pool heater for the season.

What to Check When Suction Stays Weak After Adjusting

If you rotated your pad valves or diverter plate and the skimmer still barely pulls water, the issue is usually a physical blockage or an air leak rather than a valve setting. Work through this checklist to locate the issue:

• The weir door is stuck upright: Check if the plastic hinge pins on the weir door popped out of their tracks. If the flap gets wedged against the skimmer walls, it acts like a dam, blocking pool water from entering the skimmer well and starving the pump.
• The water level is too low: If the water level drops below the midpoint of the skimmer opening, the opening draws in air alongside water. This breaks the pump prime and ruins suction. Add water until it sits halfway up the skimmer mouth.
• Debris is caught in the pump impeller: Tiny pine needles and seeds can pass through the baskets and pack tightly inside the impeller (the spinning wheel inside the pump that pulls water). Turn off the power at the breaker, open the pump basket, reach through the front tube with your fingers, and feel for packed debris inside the wheel blades.
• The pool filter needs cleaning: A dirty sand, cartridge, or diatomaceous earth filter causes high pressure inside the tank. High backpressure restricts the entire system, slowing down the speed at which the pump can pull water through the skimmers. Rinse or backwash your filter to restore proper flow rates.
• The pump lid O-ring is dry or cracked: The rubber ring sealing the clear pump lid must be clean, supple, and lubricated with silicone pool grease. A cracked or pinched O-ring lets air leak into the suction line, which weakens skimmer pull even if all valves are wide open.
• There is a clog inside the underground pipe: If twigs or clumped leaves wedge inside the pipe between the skimmer and the pump pad, water flow drops drastically. You can clear this by running an expanding rubber drain bladder on a garden hose through the pipe from the pump end back toward the skimmer.

FAQs

Why is my pool skimmer making a loud whirlpool sucking noise?

A loud sucking noise happens when your skimmer creates a water vortex that pulls air down into the plumbing. This occurs when skimmer suction is set too high or when the pool water level drops too low. To silence the noise, add water until it covers half the skimmer opening, or turn your equipment pad valve slightly toward the main drain to reduce suction at the surface.

Which hole at the bottom of a two-hole skimmer connects to the pump?

The hole located farther from the pool edge (the rear hole closest to the deck) usually connects directly to the pump intake line. The front hole closest to the pool water connects to the main drain line on the pool floor. You can verify this by turning on the pump briefly while the diverter plate is removed and checking which hole pulls downward against your hand.

Can I close my main drain completely to get maximum skimmer suction?

You can close the main drain temporarily if you need maximum suction to run a manual pool vacuum or clear heavy surface leaves. But you should avoid leaving it fully closed for normal daily operation. If leaves clog the skimmer basket while the main drain is closed, the pump will starve for water, overheat, and suffer severe motor damage.

What should I do if my three-way valve handle feels stuck and will not turn?

Never force a stuck valve handle with a wrench or hammer, as the internal diverter shaft can snap off inside the PVC body. First, loosen the thumb knob in the center of the handle. If it remains frozen, turn off the pump, unscrew the small bolts holding the valve cover plate, and lift the assembly out to clean out grit and lubricate the internal rubber seals with silicone grease.