Accumulator tanks use pressurised air to send water through a boat's lines without using the on-board water pump. This reduces the number of cycles a water pump has to produce, which cuts down on its internal motor wear. It also reduces noise, since the pump does not have to run continuously after the flush of a toilet or the opening of a fresh water tap. A bladder inside the accumulator tank creates the pressure needed to force the water through the lines. Sometimes that standing pressure can increase or decrease, requiring a simple adjustment.
Locate the accumulator tank on your vessel. It should be mounted inside a cabinet attached to the bulkhead, next to the water heater or very close to the discharge side of the water pump. Most accumulator tanks look like an upright cylinder, and come in sizes ranging from 2 gallons to 10 gallons or larger. It may be plastic or metal. Examine the fittings and lines running to it. Look for any water puddles beneath it. Use an end wrench to gently tighten the line fittings.
Refer to your boat owner's manual under the section for recommended accumulator tank pressure for your boat. Remove the Shrader valve cap on the accumulator tank and spit in the opening of the valve. Look for bubbles. If you see bubbles, it has a valve leak. Tighten the Shrader valve core pin with a tire valve tool.
Turn on the water pump switch. Have an assistant open a water faucet valve and let the water run. There should be no noise coming from the pump for 30 seconds or so. The instant the water pump cycles on, shut the water pump switch off. Place an automotive tire gauge on the tank Shrader valve and push it down to take a reading.
Note the psi (pounds per square inch) on the tire gauge and compare it with your manufacture's number. It should be close. This number represents the pump "cut-in" pressure. It it reads too high, use the tire valve tool to push the Shrader valve pin to release some air. If it reads too low, attach the hose from a bicycle pump to the Shrader valve and pump the pressure up to specifications.
Use a socket to remove the drain plug on the bottom of the accumulator tank, and let the water drain into a pan. Replace the plug. Check the air pressure in the tank again with the tire gauge. This number represents the "air charge" pressure. If the air charge pressure equals or exceeds the cut-in pressure, release more air from the tank until the air charge pressure measures slightly less than the cut-in pressure. Release the pressure in 5 psi increments until you achieve the proper setting.
Be aware that many manufacturers ship new accumulator tanks with very high pressures that must be adjusted upon installation. These are called "pre-charged" pressures, and have nothing to do with the settings for specific applications.