Water Pressure

[BobW]

On another thread a few days ago I asked about my seemingly low water pressure. I'm getting about .5 gallons/minute and was told it should be more like 2 gallons/minute.This weekend I finished installing an Accugage tank monitor. To calibrate it, I had to fill my water tank. I went topside and unscrewed the water fill plug - and noticed while I was unscrewing it that there was air hissing into the fill hose.That got me wondering about the vent, so I filled the tank ALL the way full and was rewarded with water pouring out the vent fitting in the transom. AHA, I said, obviously the vent hose is NOT blocked!The water pressure was still low, although it improved about 30% when I replaced the in-line filter. I went on to other tasks, but that hissing still bothered me.TWO DAYS later, out of the blue, it hit me: What if the vent hose has a dip in it that allows water to collect????? It seems possible that the water pump might not be powerful enough to suck the water in the vent line back into the tank, and it may not be able to get enough water fast enough to fully pressurize the system.Both the vent and fill fittings are on the side of the tank since it is under the quarterberth. I know that the fill hose has such a loop, but I'm not sure about the vent. It crosses from the port q-berth to the starboard transom, so it's quite possible.I'm so excited about this possibility that I'm even contemplating a trip to the boat (2 hrs rt) just to check it out It even occured to me that the same situation could happen in a holding tank vent, but I suspect that the massive pump-out system, which can suck a column of water up more than 6 feet, would also suck the water out of an inverted loop in the vent.Cheers,Bobs/v X SAIL R 8

 

[Peggie Hall HeadMistress]

You're definitely onto something.

The hissing sound when you opened the fill cap is a sure sign of a blocked vent. Could be a kink in the line...or it could very well be a pool of water in a low spot.You're right that the same thing can happen in a holding tank vent...and while some pumpouts may be strong enough to pull the water out of the vent before it can pull a vacuum, not all are...especially if sag in the line is low enough and if enough water or waste has collected in it. If it's waste, not water, that's collecting in a vent line, it can harden...creating a plug that NO pumpout can pull out.

 

[Steve]

Try a Shop Vac

Maybe if you take the fill cap off and use a Shop Vac over the vent to suck (or blow) any water in a low spot out. Then put the fill cap back on and run several gallons of water out of the gally sink. Slowly open the fill cap and see if you are still getting the hissing. If you don't, then you have solved the mystery -- but still need to fix the problem.

 

[BobW]

Good idea, Steve

and I'll keep it in mind (although I sold my BIG shop vac when I sold my BIG house and moved into a small apartment) - but I'm sure I can borrow one or use this as an excuse to buy one I think I'm going to start with a visual inspection of the hose, then disconnect it from the tank and test the pressure.I'm actually not too concerned about the pressure we get from the faucets, but we dive a lot and I rigged a long hose from the head out the porthole to the foredeck to use for fresh-water rinsing our gear. And that only gets a trickle!Peggy, that is my concern also regarding the holding tank vent. And it occurrs to me that the 'whiff test' - smelling the exhaust of the vent line on deck when someone else flushes the toilet - doesn't verify that the vent line is clear in this case because the gas will just bubble through the water.I will report after I get a chance to get to the boat.Cheers,Bobs/v X SAIL R 8

 

[Calif. Ted]

Seems like if you leave the fill cap open on

deck it will act as vent and if the water pressure is much improved you'll know vent is blocked. Some pumps have a screen filter on their inlet that can clog. I can hear the air venting thru sanchions when filling the water tank and from black water tank when pumping out at a dockside station. I did replace the vent line when I first got my used boat because it had a low spot & some tight bends, they can clog with "material" that may get in the line when tank full, lots of heel or rough conditions allow the liquid into the vent line.

 

[BobW]

I am sure the fill hose has a downward

loop that will collect water - it is right next to the tank (the hose is filthy on the outside, and is on the list for replacement). What I can't remember is whether there is one on the vent line.I guess my memory just ain't what it used to be.... but I'm not sure *yksCheers,Bobs/v X SAIL R 8

 

[Peggie Hall HeadMistress]

There should be a loop in water and fuel vents...

One that goes UP, not a sag that can collect water. It's to prevent rain water from getting in any time, and sea water from from getting into the tank when you're heeled enough to put the rails in the water.The holding tank vent line should not have a loop OR a sag in it...it should be straight, with a clamshell over it if necessary to prevent taking on sea water when heeled on a long tack.

 

[Rich]

don't go loopy...

I think there's some confusion here cause by old boat-manufacturing practices that don't "hold water" today, if you'll pardon the pun. I'm pretty sure the presence of loops in water and fuel lines that you'll find in older fiberglass production boats were attempts by the factory to save time and money by imitating the function of an anti-siphon valve (to prevent seawater from backing into tanks or the bilge during an extended heeling or waves lapping against the transom). The problem is the loops don't really work because they don't have the valve to control vacuum in the lines.You need to consider what type of line it is and where it's located. Using loops in a fuel line is not a practice worth considering today--insert a fuel/air separator in the vent line and get rid of the loop to the fuel tank, it's the safest and most current practice.You wouldn't design a water system to use anti-siphon valves to reduce seawater intake because you don't want even a little seawater to reach your fresh water supply; the baffled vent cap on the hull is designed to prevent any water egress at all (including rainwater)and the loop, which is just a bad imitation of an anti-siphon valve, is irrelevant and probably hurting your pressure/vacuum setup. And unlike the fuel line, where the fuel/air separator is critical to prevent spillage/pollution/fines, who cares of water overflows out the vent? Ditto with the waste, but you do want to use the same type of baffled vent just to make sure too much seawater wouldn't fill the tank. (The baffles, if the vent is not broken, should prevent any siphoning effect at all). The loops that are suggested for sinks makes somewhat more sense, but only as a backup against forgetting to close the thru-hull.

 

[Peggie Hall HeadMistress]

You're confusing two different functions...

A vented loop has TWO functions: it prevents a siphon by injecting air into a line to break the flow, and it creates a "hill" above the waterline. However, a vented loop would never be needed in a line exiting a thru-hull ABOVE the waterline, 'cuz a) there's no way for a siphon to get started...and b) water only rises to the waterline, so no "hill" is needed.The ONLY reason for loops--no special fitting, just an arch--in water and fuel lines is take advantage of the law of gravity: water runs down hill. So if the first foot of line from the through-hull runs UPhill, any water that gets into the line via the thru-hull can't run down the vent into the tank. Nor can any water or fuel from overfilling a tank sit in the vent lineAnd btw...loops--arches--in tank vent lines aren't only found on older boats. While they aren't that common in water tanks, it's rare to find a fuel tank vent line that doesn't have an arch in it.

 

[Gord May]

Trap

I think that Bob was referring to an unintended "Trap" in his vent lines - not a vented loop (which is a very different thing).Vents must 'climb' continuously to their opening./Loops, Go up, then down. ^Yep - it's plumbing, all right

 

[BobW]

Yes, Gord, the plumbing term is trap

and we are talking about plumbing, aren't we?Cheers,Bobs/v X SAIL R 8

 

[Phil]

Screen

Did you check the filter screen at the front side of the pump and the airation screens in the facet discharger? I know my new boat had tons of crap in the system which slowly clogged the screens to the point of barely a trickle.