A D I Y Self-Priming Pump From P V C Pipe

[Crossy]

OK before we start a bit of history.

Our new home has a large garden (1.5 Rai) which Wifey wants turfed as well as lots of trees and plants. In all we have about 1,500m² of grass which will eventually be turfed with the Japanese grass (SWMBO does not like the Malay stuff). Currently it's just growing whatever comes up, it's green and at present that's all that matters.

That much lawn will need a LOT of watering, luckily we live next to a khlong which is connected to the Chao Phraya so it's always got water (sometimes rather too much water) so we have a readily accessible source of water.

The original plan was to pump water from the khlong directly to the sprinkler system, however this ran in to a few difficulties, particularly when the khlong was low the pump didn't have enough flow for the sprinklers. I decided that the easy fix would be a buffer tank, pump from the khlong to the tank and then pump from the tank to the sprinklers, a 1,000L tank (cheap) was duly acquired. Unfortunately the only location available for the tank was about 50m from the khlong so a long suction was going to be needed.

The arrangement in the drawing is what we ended up with.

The positioning of the non-return valve isn't ideal (the fish basket does not have a foot valve) and the whole thing was a dog to prime, once it was primed it worked OK. Unfortunately the smallest bit of anything in the non-return valve resulted in the pump losing prime and us having to go through the whole rigmarole of priming all over.

My first attempt at a fix was to add a T just after of the non-return valve to which a hose from the domestic supply was attached, this allowed us to fill the suction with water reasonably easily. However an automatic solution was required to keep Wifey happy.

The solution is the subject of the next and subsequent posts.

[Crossy]

Obviously a real self-priming pump would be the simple solution, however they are not cheap and our budget is not infinite so I decided to have a go at DIYing something around our existing pump.

A self primer works by recycling in initial pump full of water whilst drawing air out of the suction, a fuller explanation here http://www.gongol.ne...se/selfpriming/

I initially envisioned making something along these lines, but since our pump is right next to the tank I went for the easier solution of injecting water from the tank into the suction, the water simply goes around and around drawing air from the suction with it. Eventually the suction is full and the pump operates normally.

This is what I made.

The amount of water recirculated from the tank is controlled by the valve so that not too much goes around the loop when the system is primed and pumping. In fact the restriction provided by the shower tube is sufficient so the valve is left wide open.

The real thing looks like this.

The DIY air release valve is a 1 1/2" to 3/4" reducer with a ping-pong ball inside, a wire cage stops the ball falling right down the tube when the pump is not running.

The air release valve theoretically provides an easy exit for the air drawn from the suction line, in reality it's not necessary if you have an open end to the discharge like we do.

[Crossy]

So, how well does it work? Reasonably is the answer, it takes 15 minutes to start pumping with a completely empty suction line so it's probably nowhere near as good as a real self primer. Since the suction normally doesn't empty completely even when there is a bit of weed in the lower non-return valve it usually starts pumping in a minute or two, more than fast enough to stop the tank running dry.

On the whole a successful DIY from bits we had laying around

If anyone has suggestions to make it work better, please post, as with most of my engineering (including the paying stuff) it's an ongoing development job.

[Daffy D]

Hi Crossy

Looking at your first diagram, shouldn't the non-return valve be in the water at the start of the suction pipe?

The weight of water in the vertical pipe pressing down on the valve when the pump is off would will make a better seal to stop return leakage.

[Crossy]

Yes Daffy, it should, the reason it is not is long and convoluted, just rest assured that it's no longer possible to install a proper foot valve without significant hassle and me getting VERY muddy.

EDIT Thinking about it, I could get Wifey to go in the mud, photos could be very saleable

[passingas]

This is a wee bit off the subject, but how could I do a DIY suction breaker (just the opposite of what your going through) that would allow air to enter (a 4" sewer line, with only one toilet on it) when flush water is going through and closes (the obnoxious odors) after the fact. Now it gurgles and belches after a flush and it is because of no proper venting. I used to work in a boat yard building custom yachts and we installed these vent loops on the heads where the air break was just above water line so that it could not make a siphon and sink the boat before anyone caught it happening. It has happened before, especially on sailboats. Thanks pg

[Daffy D]

As it's the wifey's lawn I think she would be only too delighted to jump in the muddy khlong and under your direction fit new valve.

As an extra incentive you can tell her that she will be TV pin-up of the month.

[jpinx]

This is a wee bit off the subject, but how could I do a DIY suction breaker (just the opposite of what your going through) that would allow air to enter (a 4" sewer line, with only one toilet on it) when flush water is going through and closes (the obnoxious odors) after the fact. Now it gurgles and belches after a flush and it is because of no proper venting. I used to work in a boat yard building custom yachts and we installed these vent loops on the heads where the air break was just above water line so that it could not make a siphon and sink the boat before anyone caught it happening. It has happened before, especially on sailboats. Thanks pg

I did the boat version with a modified caged pingpong ball valve - self sealing if the water level lifted the pingpong ball to cover the end of the pipe;)

For the domestic version just tee-off a small bore pipe and run it high enough to be above the head of any water level in the drainage system.

For the self-priming pump - the simplest way is to fit a small header tank containing enough water to prime the system twice over, and a floating stopvalve to prevent it over filling when the pump is running.

[bankruatsteve]

This is a wee bit off the subject, but how could I do a DIY suction breaker (just the opposite of what your going through) that would allow air to enter (a 4" sewer line, with only one toilet on it) when flush water is going through and closes (the obnoxious odors) after the fact. Now it gurgles and belches after a flush and it is because of no proper venting. I used to work in a boat yard building custom yachts and we installed these vent loops on the heads where the air break was just above water line so that it could not make a siphon and sink the boat before anyone caught it happening. It has happened before, especially on sailboats. Thanks pg

If your toilet "gurgles and belches" that could be from a full system - screw open the lid of your septic tank to check. You should not get the sewer smells through the toilet trap.

[passingas]

This is a wee bit off the subject, but how could I do a DIY suction breaker (just the opposite of what your going through) that would allow air to enter (a 4" sewer line, with only one toilet on it) when flush water is going through and closes (the obnoxious odors) after the fact. Now it gurgles and belches after a flush and it is because of no proper venting. I used to work in a boat yard building custom yachts and we installed these vent loops on the heads where the air break was just above water line so that it could not make a siphon and sink the boat before anyone caught it happening. It has happened before, especially on sailboats. Thanks pg

If your toilet "gurgles and belches" that could be from a full system - screw open the lid of your septic tank to check. You should not get the sewer smells through the toilet trap.

Just had it cleaned out and was hoping that was what was making it do that, however now, it is still doing it. There are no smells coming into the water closet area, but about 15 seconds after it is flushed, I can see that the water goes out of the bowl and then it does its secondary swallowing. Crossy, I didn't mean to hijack your thread...I will post this independently of yours...again, sorry about that. pg

EDIT New thread is here

Edited February 2, 2013 by Crossy

[passingas]

Crossy,

That is some very nice pipe work there...are you sure you're not a closet plumber or at least a pipe-fitter (they can chew their fingernails, you know) from another life time? I can tell the well thought-outness is engineer derived. Looks really great. pg

[Daffy D]

Hi Crossy

The other day while having my morning cup of tea quietly contemplating life the universe and everything and speculating on the forthcoming TV pin-up of the month, I suddenly had the idea why not put a upside down 'u' bend (let's call it an 'n' bend) in the intake pipe at some point before the pump.

Something like this:-

As long as the top of the 'n' bend is higher than the pump, the pump will always be primed. A bit like your solution but simpler and without the possibility of the water tank draining out if the non-return valve leaks.

The other option is to just have a regular ball valve in place of the no-return valve and just remember to turn it on and off each time.

OK back to my cup of tea

Edited February 4, 2013 by Daffy D

[thunder30101]

I put a tee and valve from the outlet line from my tank to the inlet line of my pump, open it to flood the inlet while starting the pump then close it after water starts flowing to the tank, no problems. Just always make sure to not run the tank level down below your pump level.