Author Topic: Pressure Switch (Read 20965 times)

redoverfarm · « **on:** April 12, 2010, 08:36:00 AM »

I am in preparation of setting my well pump in my remote cabin. I plan on using a Sureflow DC pump to pressurize my pressure tank and supply water to the cabin. My question is will a standard pressure switch work with DC power or will it require a DC pressure switch. I think I probably alredy know the answer that I will need a DC switch correct. Does anyone on the board know of a resource for these. Most of my experience has been with Grid tied systems so this is something new to me. Any help or suggestions will be appreciated.

There is some discussion of my project in an associated thread which is contained here

http://fieldlines.com/board/index.php/topic,133149.msg871394.html#msg871394

Thanks

John

Volvo farmer · « **Reply #1 on:** April 12, 2010, 08:48:32 AM »

What kind of Shurflo pump? a 2088? Those have a pressure switch built in that is rated for DC. We've been using the equivalent of a 2088 (but the AC version) with it's built-in pressure switch and a pressure tank for over 2 years now. The pressure is a bit lower than average neighborhood pressure but it works fine.

redoverfarm · « **Reply #2 on:** April 12, 2010, 09:00:42 AM »

Volvo as bad as it may sound I haven't decided on a particular model. I sort of feel like a small ball in the tall weeds. Any suggestions? I also take it that if I go with a 48V system that I will have to change that voltage to a 12 or 24 volt to supply the pump. That seems to be the common range of the pumps.

bob golding · « **Reply #3 on:** April 12, 2010, 10:41:46 AM »

i have a 2088 12 volt model and can confirm it does have a pressure switch. be careful with the fittings. i broke mine by dropping it with a big filter attacted to it. it still works but leaks a bit. agricultural suppliers might be the best place to look. theu use them a lot on farm sprayers.

wpowokal · « **Reply #4 on:** April 12, 2010, 11:34:05 AM »

I would go with a pump with built in pressure switch, I have worn out several sureflow pumps on spray units but never the pressure switch.

Do your power requirements necessitate 48 volt or would 24 do as 24-12 volt converters are common, unless your remote cabin power requirements are greater than 3 Kw go with 24V.

allan

hydrosun · « **Reply #5 on:** April 12, 2010, 12:02:18 PM »

The difference between an ac and dc switch is the speed that the switch opens. A dc switch has to open quickly to end the spark jumping the opening gap. Usually a strong spring snaps it open. So a AC pressure switch with spring action can be used on DC with lower rated amperage. I've used them on Dc shurflow pumps when the built in switch failed.
Shurflow pump use a rubber diaphram that will fail after 2000 hours and allow water into the motor, causing that to burn out. If you replace the diaphram before 2000 hours you can extend the life of the pump. If you want a longer lasting and lower maintainance pump you can pay more for a Sunpump SCB centrifugal booster pump. They are available in 12 ,24 and 48 volt models. I haven't used them, mainly because of price.
chris

redoverfarm · « **Reply #6 on:** April 12, 2010, 01:09:40 PM »

Allen that was the recommendations in this thread.

http://fieldlines.com/board/index.php/topic,133149.msg871394.html#msg871394

Not actually in stone but those who had 24V wished they would have went with 48V. Actually you are only looking at a few additional batteries (6v) and if the life of the batteries would probably be extended by increasing the size.

. What I am looking toward is a 3600watt inverter.

Chris I had read that some use the AC switch on a DC system but they explained the same as you had.

ghurd · « **Reply #7 on:** April 12, 2010, 01:40:20 PM »

It might be the long way around,
but could use the pressure tank's switch contacts to operate a lower voltage relay coil. Relay contacts dealing with the 48VDC power.

A properly sized resistor or Zener would take care of the 48V to lower voltage relay coil.
Plus a Schottky flyback diode on the relay coil.
Pretty simple stuff. Don't get scared off by fancy unfamiliar words.

I see it as avoiding replacing burned switch contacts.
If the relay contacts burn, simple to replace the relay.

Choose the relay carefully, and probably want to have a spare on hand. Just in case.

Not saying it is a great idea, but it would work.
Anybody have thoughts about that?
G-

Volvo farmer · « **Reply #8 on:** April 12, 2010, 10:21:18 PM »

Honestly, if you're going to have a nice beefy sinewave inverter on all the time, why go through the hassle of a DC pump? I'd argue that any savings in efficiency is going to be minimal, and the wiring and pressure switch, especially at 48V are going to be a real pain.

hydrosun · « **Reply #9 on:** April 12, 2010, 11:45:53 PM »

In the past solar panels were so expensive and inverters so small that it made sense to use the highest efficiency dc pumps. I switched to using a Grundfos submersible AC pump after experiencing the short life of dc submersible pumps. The grundfos is close to the efficiency of the dc pumps. If water needs are just for household use the power needs are small. I just figure 1 to 3 watt/ hours for each gallon of water. 100 gallons a day is 100 to 300 watts. The lower number is an efficient dc pump the higher is a standard ac pump. If you are pumping water for irrigation that uses 1000s of gallons per day it might pay for the higher efficiency.
Chris

rossw · « **Reply #10 on:** April 13, 2010, 04:39:46 PM »

When faced with the issue of a pressure-pump for my new home about 7 years ago, I initially used a shurflo-clone pump with integrated pressure switch.
First thing was, the switch just plain wasn't up to the task and failed unreasonably quickly.

I then used a stand-alone pressure switch on the line that was good for 10A and fast-acting, so I could (in the first instance) use the original pump after bypassing it's pressure switch. This worked for a time, but I was then faced with the fairly large start current, and the constant start/stop/start/stop cycling of the pump. This was particularly evident with low flows (like a single tap on gently).

I built a "constant pressure" pump using a linear pressure sensor coupled to a variable-frequency drive controller and reasonable AC pump. My first version was a temporary arrangement, and worked adequately, but the discrete parts were a poor match and performance wasn't great, but the concept was there.

I soon found a commercial pump (Lowera) that did all this and wasn't particularly expensive but works FAR better than antything with a stop/start type pressure switch. Basically, the pump will run only as hard as it needs to to maintain the water pressure at the value you have set. So with one tap on, the motor just ticks over slowly and uses very little power. With everyone having showers and the hoses running, it runs much harder - and everyone gets the full pressure! It's kind to the batteries (it starts and stops gently), it's kind to the pipes (no water-hammer), all round good solution.

Click images for higher-res versions.
[img width= height=]http://house.albury.net.au/04jun2005/thumb.MVC-879X.JPG[/img]old pressure switch and gauge, with new pressure sensor on 'T
'[img width= height=]http://house.albury.net.au/04jun2005/thumb.MVC-880X.JPG[/img]New Pump
[img width= height=]http://house.albury.net.au/04jun2005/thumb.MVC-881X.JPG[/img]Side view of pump

redoverfarm · « **Reply #11 on:** April 13, 2010, 05:10:28 PM »

RossW how hard on the batteries is your Lowara pump. It appears that you have it to a pressure switch (AC/DC?) Same goes for the pump AC or DC? And the most important question is $$$?

WindriderNM · « **Reply #12 on:** September 01, 2010, 12:19:18 PM »

How about putting a capacitor across the contacts to decrease arcing (remember the old ignition systems with points for cars)

rossw · « **Reply #13 on:** September 01, 2010, 10:06:12 PM »

Quote from: redoverfarm on April 13, 2010, 05:10:28 PM

RossW how hard on the batteries is your Lowara pump. It appears that you have it to a pressure switch (AC/DC?) Same goes for the pump AC or DC? And the most important question is $$$?

Sorry, I didn't see this until just now!

The Lowara is fantastic. It's set to keep the household water at 60 PSI, regardless if it's one toilet slowly refilling or 3 showers running, the washing machine filling and a hose running outside. And it does.... I think it's good to about 50 litres/minute.

It can take up to about 1.5KW if it's going flat out, but most of the time it just ticks over and takes a few hundred watts. It's a soft-start and soft-stop, so it ramps up and down rather than just kicking in and pulling insane amps when starting.

It was expensive, but it was pretty much the only one I could get in .au at the time, and attracted a premium price. Nowdays I think you can get them much much cheaper. Ask around, check ebay and other online sellers. Play one supplier against another and I wouldn't mind betting you can get one of these for about the same as a nasty old stop/go clunker.

hydrosun · « **Reply #14 on:** September 02, 2010, 10:39:30 AM »

The grundfos sub pump can also be used with a constant pressure controller. I bought one on ebay for our farm on the grid but haven't hooked it up yet so I don't have any data on it's performance.
Chris

Volvo farmer · « **Reply #15 on:** September 02, 2010, 11:50:25 AM »

Quote from: rossw

It was expensive, but it was pretty much the only one I could get in .au at the time, and attracted a premium price. Nowdays I think you can get them much much cheaper. Ask around, check ebay and other online sellers. Play one supplier against another and I wouldn't mind betting you can get one of these for about the same as a nasty old stop/go clunker.

Is there some reason you don't want to use a large pressure tank with that system? My first pump was a spendy Grundfoss variable speed and it drove me crazy because it came on and used power any time I had a faucet open, even a trickle. My $700 pump now sits on a shelf in storage and the 32 gallon pressure tank I now use will give 10 gallons of water from 50 to 30 psi in between pump cycles. This old shurflo 2088 has been in service 3 years now and only costs $120 new. I only get about 3GPM out of it but vastly prefer being able to flush a toilet without the pump coming on every single time.

Shadow · « **Reply #16 on:** September 05, 2010, 05:50:37 PM »

I've been using a Shurflo Extreme series, 6-7 gpm at 60 psi. with a 15 gal pressure tank. It has a built in pressure switch but I dont use it. I use the regular pressure pump switch.

I have a 48 volt system but use a voltage reducer to 12 volts to run the pump. Going strong into our fourth year. It to will keep up with showers, toilet flushes and washing machines.

I found the built in pressure switch didnt always shut off cleanly, it would slowly still turn the pump until the pump got hot. At least with a pressure switch you can hear it click on and off.I think we keep our settings about 40off to 25 psi on.

SteveCH · « **Reply #17 on:** September 08, 2010, 08:15:54 AM »

When I bought my Flowlight pump [Dankoff] over 20 yr. ago, it came with a kit of hardware to plumb it into the water system, pressure tank, etc. The switch is a Pumptrol and I had to replace it once after 12 yr. or so. Found the exact switch at a local hardware store for $14 or something like that. It is good for ac or dc. Works great. Simple and available anywhere.

just-doug · « **Reply #18 on:** February 26, 2011, 11:52:50 PM »

i use the sureflow pumps.the stock pump switch doesn't hold up to a lot of on off cycling,a surge/pressure tank helps pump life.i went to the hardware store and bought a 220 ac pumpswitch.in the fine print it was actually rated for 39 volts dc and 1/8 hp i believe.i used one set of contacts.if they ever ware-out,ill just move over to the other set,since 220 uses two sets.cost was about 15 dollars.been about 7 years ago and still on first contacks

redoverfarm · « **Reply #19 on:** September 13, 2011, 04:59:50 PM »

Well it has been some time since my initial inquiry and conversation. Just to bring those who helped up to speed with my cabin project, power supply and water. I have conquered all of those with the installation of a Grundfos 5SQ07-270 pump which is a slow start model with a 8.4 amp draw. The pump when tested drew 6-1/2 gpm at 210 feet. Good enough.

The power system is a 48 volt system, powered by a Magnum MS4448PAE inverter, accompanied by a Mini Magnum Panel, Automatic Generator Start, Battery Monitor and last but not least a Generac EcoGen 5818 generator. I got it up an running last Friday and still have a few modifications but all in all it is working fine.

Thanks for all your help

rossw · « **Reply #20 on:** September 13, 2011, 05:55:26 PM »

Just a small observation - it's good to see a fire extinguisher there - but I would be more comfortable if it was not in the middle of the area that's most likely to be on fire itself!

I have one in the generator room, and one in the battery/inverter room, each are right by the entry doors and well away from the action in the event I ever need to use it.

WindriderNM · « **Reply #21 on:** September 13, 2011, 06:13:25 PM »

If you are still looking for a pressure switch I have 2 Meletron 0.5-80 psi pressure switchs # 420-20L
with Common/NO/NC wires listed on ebay #220841591430 and #220766584287

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Author Topic: Pressure Switch (Read 20965 times)