Hello Jan,
Without knowing the type of non-return valves, and without seeing a schematic of the installation, I can only offer comment in generic terms:
- the moving or flexible component of all simple non-return valves will be made of a synthetic "rubber-like" material, ideally nitrile, possibly neoprene.
- as such, they will all be subject to age hardening ie they will become stiffer over time, and may take a set in an open position, or and/or no longer open fully. Ultimately they may crack and break.
- however, long before this point,
scale and other deposits are likely to have built up on them, which will of itself make them stiffer or even ineffective.- you can try introducing acetic acid [vinegar] or more expensive proprietary chemicals, but
the quickest, simplest, cheapest and most effective solution is simply to take them apart and scrub them clean in hot water!
- then examine them, and if they are now soft and flexible, and without visible cracks or damage, re-assemble them and they will work as originally intended.- as to how well they work, that is very often a function of the way in which the pipework runs are installed - which in turn is a function of whether the original builder/installer really understood how to install them in order to achieve whatever was his objective...
- your complaint only refers to the sinks not draining properly rather than about seawater flooding in, but if they aren't draining properly, then they almost certainly won't prevent seawater flooding in either!- if the actual "rubber" valve itself is a more modern cone shape terminating in a Y shaped slit [tricuspoid or "aortic" like a modern toilet and bilge pump valves], then pipework that falls continuously to the skin fitting is fine, but if the valve is a simple flap valve, then it needs to be installed in the Uphill side of an S bend so that gravity holds it shut except when the weight of water leaving the sink pushes it open. Otherwise, gravity will cause the valve to "droop" and age hardening will cause it to "take a set" in this drooped or open position, and when the boat heels, and seawater comes up the pipe, it may well simply flow straight past the open valve, rather than pressing it shut as designed.
- in any event, bear in mind that all these simple so-called non-return valves are very crude affairs - not like a seacock - and can never be relied upon to prevent the ingress of water in the same way as a valve which has a manually operated closing mechanism.
Geoff Sheddick
Parker 27/146 "Stroller'
Geoff Sheddick
Parker 27/146 "Stroller'