An accumulator is an important part of the pressurised fresh water system for an American RV motorhome.
The purpose of the accumulator is to act as a pressure buffer when fitted close to the water pump outlet. Some American RV motorhomes are fitted with an accumulator, while some are not.
If your American motorhome has not been fitted with one and you turn the tap partially on you will hear the water pump cycle off and on, then the water flow from the tap will increase and decrease as the fresh water pump cycles.
The disadvantage of not having an accumulator in the system is that the frequent cycling of the fresh water pump causes the water pump pressure relay to fail prematurely. This cycling also causes the tap water pressure to be erratic and the shower water temperature will not stay constant.
Accumulators work by balancing the water pressure with the fresh water pump delivery. One-half of the accumulator contains a rubber diaphragm which has a Schrader valve connection on its body, allowing you to adjust the air pressure to about 3lb/SQ.” below the cut in pressure of the fresh water pump. When the accumulator is fitted just in front of the fresh water pump outlet, the air pressure in the diaphragm allows the water to flow from the accumulator without surging.
Most fresh water pumps deliver the fresh water at a maximum of 45lb/sq.” and the pump will restart when the water pressure reaches about 30lb/SQ.” The water pressure acts against the diaphragm in the accumulator to give you a smooth flow of water from your tap.