I like the idea of constant water pressure, but how best to achieve it. Currently have a Davey pressure pump with pressure tank but am sick of adjusting the shower 15 times while showering. It's worse now that the solar water is so hot. ( I have a tempering valve ready to fit, another story). The Grunfos CME pump changes speed to suit the flow which seems a good idea, but what about the other cheaper constant pressure pumps? Do they change speed or simply have some sort of pressure/flow regulator while running at a constant speed? Would go for the Grundfos but at around $1500 it's a bit pricey, considering that he pump I have hasn't failed and isn't likely to do so soon.
Variable speed pressure pumps.
(14 posts) (7 voices)-
Johnnojack
MemberPosted Saturday 31 Dec 2016 @ 6:15:02 am from IP # -
APR
MemberJohnnojack said:
I like the idea of constant water pressure, but how best to achieve it. Currently have a Davey pressure pump with pressure tank but am sick of adjusting the shower 15 times while showering.Fit a Davey Torrium controller to your existing pump.....
http://www.davey.com.au/media/custom/upload/Torrium2_Plug_Play_Datasheet_DWP0844.pdf
Posted Saturday 31 Dec 2016 @ 1:34:20 pm from IP # -
Greg
MemberI've had a bad run with pressure tanks and am now looking for alternatives. Looking at a cycle stop valve. Have a Google and see what you think. Can never tell if marketing is true but if this 3rd bladder has gone (just out of warranty) I'm not spending $700 to replace it. The csv option looks like it would solve most of the problems.
Posted Sunday 1 Jan 2017 @ 9:15:52 pm from IP # -
dax
MemberWe use cheap ebay pressure pumps, never a problem and they are so cheap you can have a couple of spares. We tossed the expensive brand pumps, they never live up to their claims for the cost.
Something like these work well for many years, the one on the houses has been there since I got on to ebay which is well over 10 years ago and have yet to use the spare ones. The provide great water pressure and feed to houses from the one pump, which sits about 5m below one house and about 10m below the other one
For gardens we use these and they seem to last, still haven't had to use the spares
http://www.ebay.com.au/itm/Electric-Clean-Water-Pressure-Pump-GardenPosted Sunday 1 Jan 2017 @ 10:21:12 pm from IP # -
Johnnojack
MemberQu. These cheap little pumps, I assume to keep constant pressure they simply throttle the outlet from the pump, rather than slow down the motor, is that right? If yes then they keep running at 2850rpm whenever a tap is on, correct? I have one similar, a Bianco pumpZ but it needs a couple of bits to get it working, has the controller, is it worth the trouble? Dax?
Posted Tuesday 3 Jan 2017 @ 3:30:14 am from IP # -
dax
MemberNot having looked at the technical aspect of the pumps, can't be sure as they work satisfactory for us and one pump runs 2 houses. But my understanding and experience is they pump until the pressure is equalised throughout the system and then switch off completely. When you turn a couple of taps on, it seems to equalise the output, but nowhere near as much as mains pressure would.
Are you still running your vehicles on BD or SVO Johnnojack.
Posted Tuesday 3 Jan 2017 @ 6:57:55 am from IP # -
Johnnojack
Member -
Hi Johnnojack, sorry I am late replying to your thread.
Firstly...the Davey Torrium controller. Unless they have very recently updated it, you have to be aware that it causes the pump to 'run on' for maybe 30 seconds after the flow demand ceases.
Pressure tanks are great for reducing a pump's start/stops which increases the pump's life span and reduces energy use but if you are off the water grid, then you need to have a good size pressure tank that is boosted to a decent pressure to reduce pressure fluctuations.
At a guess, I will say that your Davey pressure tank is set at 19 psi and the cut in - cut out pressure settings are about 20-40 psi. To reduce pressure fluctuations, the tank's pressure needs to be increased but the amount of increase depends on the size of the pump and unless you have an adjustable manual pressure controller, you will also have to buy another pressure controller to suit.
The link below is to an automatic pressure controller that is adjustable.
http://www.theirrigationshop.com.au/shopping/proddetail.asp?prod=781
The reason you will have less pressure fluctuation if you (if possible with your pump) increased the tank's pressure let's say X2 to 38 psi is because it takes X4 the head to double the flow rate and so a difference between 19-39 and 38-58 will see a lesser effect with the same 20 psi pressure fluctuation at the higher range.
A pressure tank's pressure should be checked every 6 months and topped up if needed by switching the power and water supply off and emptying the tank first. Failure to maintain the correct pressure is the prime reason for the pump short cycling and pressure tank failure.
A pressure pump not fitted with a pressure tank has a hard life because it has an energy spike when it starts that can be X3 or X4 the normal operating load and if it starts in order to supply a low flow demand, it will effectively dead head, causing a pressure wave that is referred to as water hammer. The bigger the pump and the lower the flow demand is, the greater the pressure wave will be. Pressure tanks absorb the pressure wave because they have a low level when the pump starts.
Dead heading a pump can cause severe shaft deflection that generates excessive heat and damage to the mechanical seal, bearings, wear rings and impeller and is a prime cause of premature pump failure.
IMHO (hehe), if you are off the water grid, you should have a variable speed pump for the following reasons.
No pressure variation.
Soft start...easy on the pump and no power spike or water hammer.
Considerably longer pump life.
Energy efficient. A centrifugal pump requires X8 the power to double its speed and so running even 20% slower will halve the energy requirement.
Less noise at lower revs.
Grundfos have always produced very good pumps and they are heavily into Variable Speed Drives (VSDs) and yes, the pumps can be expensive but they released a new pump a couple of months ago called the Scala2 that is variable speed drive, powerful, compact, energy efficient and it can currently be bought for as low as $900. Simply amazing value!
http://www.grundfos.com/products/find-product/scala2.html
If you look at the comparable cost of a decent pump and pressure tank with the correct pressure controller Vs the Scala2 benefits and energy savings, how could you not consider the Scala 2? It is packed with features, water cooled magnetic motor (DC?), very quiet operation, compact, simple to use and install, low energy use, long life...a brilliant pump that should suit 95% of all off (water) grid houses.
Posted Friday 27 Jan 2017 @ 10:34:00 pm from IP # -
Johnnojack
MemberHi Diver. Thanks for you detailed reply. The pump I have is a Davey dynajet50 I think. It is 22 years old and has 20l 2nd hand Grunfos tank. I did try upping the start pressure but it seems to be no better. Doesn't help that the solar hot water is so hot it has to run at 1/5 the flow of the cold to have a good shower. I have looked at the Scala but thought it looks a bit cheap and plasticy for a Grundfos. I like the CME 1-44 it has stainless pump body etc. however it isn't recommended for lifting from an underground tank, I don't know why. I have an old 250 litre hot water tank (actually never used as a hot water tank) and want to use it as a pressure vessel. I know I will need to monitor the air level and top it up from time to time but have that sorted. With a big pressure tank maybe a decent shower can be had.
The variable speed is achieved by a device which changes the frequency to the pump motor, so it seems it is still an AC motor. Any experts on this care to elaborate?Posted Saturday 28 Jan 2017 @ 11:48:44 am from IP # -
A variable speed drive can/will have trouble drawing from an underground tank if running at low speed. I didn't know that you had an underground tank, a jet pump which you have is your best option.
The CME 1-44 is several hundred dollars more than the Scala2 but rated to only 1 metre suction head, interesting and surprising. Value for money, I think that the Scala2 is excellent.
Your 20 litre pressure tank will have about 6 litres draw down. A Davey manual D pressure controller is adjustable and you could lower the 20 psi range between cut in - cut out a little but yeah, the maths with the solar don't appear to be good. Manual pressure controllers don't have run dry protection.
In some circumstances you just have to have a pressure pump on its own and another on standby. I actually have a Davey pump with a pressure tank, they are 18 years old, never needed servicing and still going strong but they are not for all of house use. I don't like Davey's policy of not allowing the retailers to advertise prices and I don't recommended them now for that reason.
Posted Saturday 28 Jan 2017 @ 12:54:49 pm from IP # -
Johnnojack
MemberSome months ago I set up a 250 litre HWS tank as a pressure tank to smooth out pressure from my Davey pump. I can report it has been a big success. Previously as Diver suggested I was getting just 6 litres per cycle with the old 20 l pressure tank. I now get 54 litres. Instead of starting and stopping several times during a shower it either starts once or not at all.
The pump runs for 3minutes to fill the tank but only cycles one ninth of the times it did before. Taking 3 minutes to build pressure instead of about 20 seconds gives much steadier pressure at the taps. This makes for a pleasant experience under the shower, finally. No diaphragm in the tank of course and the air slowly is dissolved by the water, but a minute with the compressor every 3 or 4 months keeps it topped up.Posted Thursday 5 Apr 2018 @ 1:10:59 pm from IP # -
scott drew
MemberJohnnojack,
To clarify. ..
You have your pump leading to pressure vessel (old hot water system) which then heads off to the rest of the house ie hot water system/ normal taps etc.
What modifications did you do to the pressure vessel? Ie dud you have to shorten the existing outlet so that you can get the "bubble" or air to stay available for pressurisation? Did you do anything with the sacrificial anode, if it had one? How do you get the air in there with the compressor?
Posted Friday 6 Apr 2018 @ 5:15:50 am from IP # -
Johnnojack
MemberOk will try to answer now the forum seems to be working again.
I did not use the existing outlet as it is near the top, I welded a fitting into the hole where the element was as it was the lowest opening.
The anode has been left as it was. I fitted a sight tube from top to bottom to be able to see the water level. At the top of the sight tube there is a tee fitting where I have brazed in a Schrader valve (tyre valve). When the tank is nearly empty the tank has 30 psi in it and the pump is set to start at that pressure. It shuts off at 42 psi and the water level reaches a mark by the sight tube. This is about one third up from the bottom. When the air dissolves the water level rises above this mark and I then need to top up the air supply through the tyre valve. This task could be left for six months without reducing the amount of pressured water more than 2 or 3 litres.Posted Sunday 8 Apr 2018 @ 9:49:25 am from IP #
