Variable speed water pump (or at least quiet)?

[RaymondR]

Originally Posted by s/v Jedi

The variable speed pumps slow down before coming to a stop, which eliminates water hammer. We do have dampeners at the solenoid valves for the toilets though.

On reciprocating pumps pressure waves, commonly known as "water hammer" occur on both the suction and discharge side of the pump. On large pumps where the phenomena is extreme they are mitigated by both suction and discharge pulsation dampeners.

The devices sold in plumbing stores are intended for use where the rapid closure of a valve in a water pipe results in a pressure wave however they are similar in construction to pulsation dampeners in encompassing a gas chamber which expands and contracts to absorb the fluid pulses thereby preventing their further transmission.

The mathematics of the phenomena can be found in fluid mechanics handbooks under the title "the celerity of a pressure wave".

The rapid ac and deceleration of the fluid being pumped is also the cause of the high vibration levels experienced by the pump. The transmission of these vibrations through non vibration isolated pump mounting feet into the vessels structure, particularly if mounted on any flexible plywood panel, is another cause of the excessive noise.

All sound transmission occurs (no one can hear you scream in space) via the transmission of pressure waves. Dampen the wave at source, whether in solid,liquid or gas, and you will dampen the resulting noise.

The pressure waves resulting from a positive displacement pump can also be lessened by the design of the pump and this is commonly achieved by having each pumping chamber reduced in volume whilst increasing the number of pumping chambers hence quintriplex replacing triplex designs with the same output volumes.