Water filters siphon out problem

[nomand]

Hi all, I have an issue with my very simple water filtration system setup.
A whale MK3 foot pump is pulling water from the bladder and pushes it through 2 filters and up through the tap.
The filters are standard 10" cartridges, 1micron and 0.5micron sediment taste and bacterial.



I'm having the following issues:
1. The foot lever is slow to return. Feels like the spring isn't strong enough to re-prime the pump.
2. The water keeps flowing for quite some time after mechanical pumping action has stopped. I would have assumed that the flow of water is closed when the pump is not in operation, which is not the case! When inspecting the pump, it seems that it is open by default (even the manual suggests it can be plumed in series with an electric pump). Those of you who have them plumbed for saltwater sinks watch out!
Anyway, current assumption is that the pump pressurizes the filter housings and they slowly depressurize by pushing water out.
3. After little use, the water flow catches on and siphons the entire filter housing out, which than makes it impossible to pump any more water through once the system is filled with air.
I've inspected and pressurized every joint from bladder to tap and there are no air leaks I can find. The only thing I haven't taken apart is the pump itself, though shining a flashlight through it doesn't reveal much air in the housing.


Would appreciate any pointers.
Cheers!

[Weatherbird]

The pump works on both the downstroke and the upstroke. It's returning slowly due to a restriction, likely caused by the filters.

If water is still flowing after the pedal is fully up, then there is something generating pressure in the system. If you have a bladder style water tank then there could be something pushing against it creating this pressure. The bladder could also have air trapped inside that is expanding due to temperature change. I would look there first.

[thinwater]

Foot pumps do not work with 0.5 micron filters. You need a pressurized system (>30 psi) for that. The flow rating is based on 30-60 psi, depending on the filter. Two filters in series like that, no chance. A Whale Babyfoot and mk 3 are both rated at only 4-5 psi.

Few pumps are designed to stop the water flow. Certain PD designs, but not diaphragm pumps.

You need a considerable system redesign. Either pressure with expansion tank, or a single low restriction filter (treat water with chlorine followed by removal with GAC). And if the tank is above the faucet, a valve to stop siphoning ... or lower the tank.


With a foot pump you are better off with no filter and a Brita. Seriously.

[Weatherbird]

Originally Posted by thinwater

Foot pumps do not work with 0.5 micron filters.

This is not correct. I've been using a mk3 with a 0.5 micron filter for all drinking and cooking water for two people living aboard full-time for 1.5 years with no problems.

[thinwater]

Originally Posted by Weatherbird

This is not correct. I've been using a mk3 with a 0.5 micron filter for all drinking and cooking water for two people living aboard full-time for 1.5 years with no problems.

Correction. "Foot pumps do not work with most 0.5 micron filters." Many sailors have tried this and reported problems, and you are the first to report that it worked for them.

What specific filter? There are many. I'm pretty sure a common 0.5 micron carbon block filter won't work, since I have tested that, or at least it restricted the flow too much for my satisfaction.

[Weatherbird]

Originally Posted by thinwater

What specific filter?

We're using a Pentair Pentek CFBC-10. There's probably a 50% reduction in flow. I wouldn't use it as the only water source on the boat, but for cooking and drinking and as a backup when I'm working on the automatic pump it has been great.

[nomand]

Thanks for the input everyone!

Update:

I have removed a second filter to diagnose the problem and am now only using 1 housing with a 1 micron filter in it.

In the process I discovered that the Whale pump had it's lever pin displaced making the pumping less effective overall, however that wasn't the cause of the issues above.
Removing one of the filters helped, however the 1 micron is still enough resistance to pressurize the housing and allow water to keep siphoning out after pumping action stopped.

To further diagnose that issue I've removed the filter completely to see how the pump behaves without obstruction and honestly, it doesn't feel much different without the filter once the housing is full of water.

This leads me to believe the filter may contribute to the siphoning problem, but the pump is the main problem and needs service (perhaps cracks in membrane letting air through or the spring is tired) because the salt water sink pump is operating beautifully with even flow and strong return.

I will service the pump and compare with and without the filter and update my findings!

[nomand]

Another update.

I have replaced the pump with a brand new one of the same type to eliminate the pump being an issue. Our old one is many years old.

In the process I discovered a variable that was not considered previously - water level.
When water level is low in our bladder, the bladder sags onto itself and the lining partially blocks the outlet port, which contributes to the poor pump suction and return. This is made obvious by old and new pump operating the same (tight on both strokes) when water level is low and similar when water is full, though the spring in new pump is less tired and returns smoother. And that is both with and without filter.

Basically at this stage the remaining problem is the water flow after pumping action is stopped, which is less to do with siphon effect and is caused by filter housing being pressurized and it keeps pushing water out until pressure equalizes. This can be intervened by releasing pressure from the filter housing using the pressure release valve, which of course is not the solution at all.

So it seems like I need to find better filter cartridges that don't restrict the flow as much or settle for less filtration, which isn't my preferred outcome.

Swapping to a pressurized water system is not an option at this stage.

Any other suggestions appreciated!