Piston water pumps - why are they better?

train82499train82499 Registered Users Posts: 11
Am thinking of going to on demand system, and changing from water storage tank and RV pump to boost pressure. ONe of the posts here covered a number of topics and included an interesting discussion of piston pumps - which I gather are different from displacement (shallow well and maybe some deep well?) and centrifugal pumps (Grundfos eg). It was mentioned that a piston pump is really good in that is uses little power and works well, but that were hard to find. Anyway, I found this link http://earthmovement.net/FMC_Bean_Pumps/FMC_Piston_Pumps/duplex.html which covers a lot of different pumps, including piston pumps and wonder why they would draw less power and whether they are really worth considering in a solar system like mine? Basically I have a battery bank and panels on the roof and an outback 3524 but set for weekend use primarily as it is a cottage.

Comments

  • mike95490mike95490 Solar Expert Posts: 8,610 ✭✭✭✭✭
    Re: Piston water pumps - why are they better?

    piston pumps are fixed displacement, and if you "lessen the load" elevation, you get no increased flow rate, but maybe less of a amp draw.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • train82499train82499 Registered Users Posts: 11
    Re: Piston water pumps - why are they better?

    Interesting. Those pumps speak of putting out 500 to 900 PSI. You could run hydraulics on that! Maybe they are not for solar, but it is a solar type friendly web page.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Piston water pumps - why are they better?

    Piston pumps are not "better" or "worse", depends on the application.

    Piston pumps can pump very long distances and/or to very high elevations. One system we sold a few years ago with a Dankoff pump sent water 1300 verticle feet up the side of a mountain from a small spring.
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Piston water pumps - why are they better?

    If you need the pressure then piston type are best.

    I have never really heard of anyone using piston where a centrifugal pump would do. The centrifugal pump is relatively maintenance free and one (piston type) is far more prone to giving problems.
  • peakbaggerpeakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Piston water pumps - why are they better?

    Piston pumps are positive displacement pumps that are tend to be very efficient. Assuming the seals and castings are built heavy duty enough, they can pump at any pressure as long as the driver is big enough. The flow is directly related to pump speed. Centrifugal pumps have to pump to a curve where pressure developed is directly related to flow. Centrifugal pumps are relatively inefficient especially when operating outside of window of ideal flow and pressure. They tend to last longer as there is no internal moving contact except for the shaft seal. A piston pump is going to have constant slding friction between a moving piston and a stationary pump body. There are also going to be some inlet and outlet flow checks that are also potential wear items.

    So the trade off is reliability vs pump efficiency.
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Piston water pumps - why are they better?

    1) Never place a check valve on the inlet of a centrifugal pump. Chances of problems are great and usually lead to a fried pump.

    2) An outlet check valve made be required due to the application and piping configuration. The valve (if good quality and correctly installed) should be no problem.

    3) It is 100% correct that centrifugal pumps should be carefully selected for the application. Trying to reuse an old pump almost always costs you more power than the pump value very quickly.

    Russ
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Piston water pumps - why are they better?

    I replaced a 3/4 hp Centrifugal pump last year with a 5.5 gpm @60 psi Diaphragm Pump. It is a new soft start pulsed pump and only pulls 10 amp @ 12v dc. It has a 5 diaphragm head. With a transducer instead of on/off switch, it's much more efficient.

    The pump I replaced cost over $1,000 and pulled 11 amps @ 120 V, 110 + amps dc. While it would deliver 20 gpm @ 40 psi, at 60 psi it dropped to 1.2 gpm. You have to look at the pumping curve for the pump you choose and make sure it fit's what your trying to do.

    I find it hard to believe I had a 3000W inverter and maintained a 1,000 amp hr bank of batteries for 20 years to run the wrong pump and there was a $150.00 pump that pulls 10 amp dc to do the same job better.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Piston water pumps - why are they better?
    russ wrote: »
    1) Never place a check valve on the inlet of a centrifugal pump. Chances of problems are great and usually lead to a fried pump.

    In a shallow-well application there will be a check valve on the inlet side. It's called a "foot valve". It's there to keep the water in the line from leaking back into he sump.
    2) An outlet check valve made be required due to the application and piping configuration. The valve (if good quality and correctly installed) should be no problem.

    True. Not typical for applications, though.
    3) It is 100% correct that centrifugal pumps should be carefully selected for the application. Trying to reuse an old pump almost always costs you more power than the pump value very quickly.

    Russ

    Absolutely! The number of incorrectly sized pumps I've seen over the years ... Whoo-boy! :p
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Piston water pumps - why are they better?

    Piston pumps are positive displacement meaning there is no "slosh" in the process making them efficient and you can run them slow as in directly off whatever power you happen to be getting from your PV at the moment. The downside is they have tight clearances, seals, and wear so are subject to damage from dirty water.
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Piston water pumps - why are they better?

    I don't consider a foot valve as a check valve at the pump inlet I guess (even though it is) Just my strange way to look at it I guess - any restriction in a pump inlet that is not essential for system operation is trouble looking for a place to happen.

    I have never used diaphragm pumps except in very dirty water (slurry) applications and even then they were last choice.

    Something I need to learn more about.

    Russ
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Piston water pumps - why are they better?

    An excellent site that puts out a news letter about pumps with informative articles is

    http://www.lawrencepumps.com/index.htm

    Russ
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Piston water pumps - why are they better?

    I have had diaphragm pumps for many years in the Marine area for fresh water systems. The big breakthrough came a couple years ago as the number of chambers was increased to 5 and they became variable speed with a soft start.

    With 5 gpm open flow and 3.2 @ 60 psi you no longer get the pulsing and the flow is unbelievable. They are truly a " On Demand " without the need for a pressure storage tank. In fact if you have a limited water supply to draw from you almost need to use a restricter in some outlets. These pumps will allow you to run 3-4 fixtures at the same time.

    As was mentioned in the past, the inlet and outlet of these pumps should have a flex line.

    http://www.aquatec.com/aquajet-rves-pumps.html


    Search : Aquajet RV Variable Speed Water Pump
  • 706jim706jim Solar Expert Posts: 298 ✭✭✭
    Re: Piston water pumps - why are they better?

    A cast iron piston pump will last a LONG time.

    Perhaps a comparison might be a Honda EU 2000 and a 3kw Lister diesel genset; both units with similar output ratings.

    The Honda weighs 46 lb and the Lister perhaps 800lb.

    There is obviously some benefit to the heavier unit when it ocmes to longevity.
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Piston water pumps - why are they better?
    706jim wrote: »
    A cast iron piston pump will last a LONG time.

    Perhaps a comparison might be a Honda EU 2000 and a 3kw Lister diesel genset; both units with similar output ratings.

    The Honda weighs 46 lb and the Lister perhaps 800lb.

    There is obviously some benefit to the heavier unit when it comes to longevity.
    My avatar photo is of the dual piston, gear driven pump I use for all my domestic water needs. Weighs in at around 80 pounds of cast iron, driven by a vertically mounted 1/4 hp motor. It's from the early to mid 1950's, made by Beatty Brs, Fergus Ontario Canada, and belonged to my grandfather. It has supplied water to 5 generations of my family and still today, operates perfectly, like new. Replaced the 8 rubber disc valves and piston leathers about 6 years ago, so it should be good for another 5 or 10 years before they need replacing again. Actually the rubber valves can be flipped over and they're good for another 10 years. This pump will still be going strong long after I'm gone from this earth.
    They really don't make them like that any more!
    Photos here: http://forum.solar-electric.com/album.php?albumid=37
  • solar_davesolar_dave Solar Expert Posts: 2,348 ✭✭✭✭
    Re: Piston water pumps - why are they better?

    hard to beat the design of heavy cast iron, slow speeds and simple oil gearbox/crankshaft.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Piston water pumps - why are they better?
    solar_dave wrote: »
    hard to beat the design of heavy cast iron, slow speeds and simple oil gearbox/crankshaft.

    Which is why they are so uncommon: hard to sell something that costs so much more and doesn't need replacing as often. "Bad business model". :roll:
  • solar_davesolar_dave Solar Expert Posts: 2,348 ✭✭✭✭
    Re: Piston water pumps - why are they better?
    Which is why they are so uncommon: hard to sell something that costs so much more and doesn't need replacing as often. "Bad business model". :roll:

    True but it isn't always about price either. Value comes into play in products as well, as we see in the charge controller market. Make a good product and they will beat your door down.
  • jonrjonr Solar Expert Posts: 1,360 ✭✭✭✭
    I suggest that a slow piston pump has a very uneven/cylical current draw which may not play well with some current sources. And adds to wire losses.

    I am available for custom hardware/firmware development

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    jonr wrote: »
    I suggest that a slow piston pump has a very uneven/cylical current draw which may not play well with some current sources. And adds to wire losses.

    Yes, you might think that, but reality is otherwise. The greatest peak power draws of my piston pump is roughly half that of the continuous draw of a similarly flow/pressure rated centrifugal pump. AND, if an inverter can't handle the relatively slowly changing load of a piston pump, the inverter, to put it mildly, is a true POS that might blow up if a couple of 100 watt light bulb are turned on or off.
  • jonrjonr Solar Expert Posts: 1,360 ✭✭✭✭
    That's one example, but when I looked at a slow turning, single piston pump driven directly from panels (no battery or inverter) and a long wire run, it looked to be a significant problem.

    I am available for custom hardware/firmware development

  • BB.BB. Super Moderators, Administrators Posts: 30,050 admin
    You have to size the panels to the maximum power (torque)/current needed by the pump. Probably still cheaper than doing a whole panel+battery+charge controller+AC inverter (or DC direct) pumping system.

    For better or worse, batteries and energy storage are still the bane of Off Grid power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 1,360 ✭✭✭✭
    I think that a startup where the piston is just starting a compression stroke is the worse case. Once running, the mass of the pulley would help.

    I am available for custom hardware/firmware development

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    jonr wrote: »
    I think that a startup where the piston is just starting a compression stroke is the worse case. Once running, the mass of the pulley would help.

    The difference, in actual use, is not a concern. If you want to see a relatively huge startup surge, monitor the start of a centrifugal / jet pump as it sucks back the power getting it's impeller and the water it's acting on, up to speed. The exception would be those with VFD slow start capabilities.
    If you notice the little photo above my name to the left, you'll see there is no pulley, it's direct gear driven. It's motor, mounted vertically on the right, is 1/4 hp. This pump was first put into service circa mid 1950s and still operating like new this very day, supplying all my domestic water needs. NOT kidding or joking. Unfortunately they're long long gone out of production.
  • jonrjonr Solar Expert Posts: 1,360 ✭✭✭✭
    Might be interesting if I could actually buy one for a reasonable price (including shipping). Otherwise I'm going to try a small brushless DC gear pump.

    I am available for custom hardware/firmware development

  • 706jim706jim Solar Expert Posts: 298 ✭✭✭
    Some other considerations for a piston pump:
    They are the absolute best for repriming themselves, particularly when compared to centrifugal pumps. Anyone who has ever suffered with a balky pump will appreciate this ability.
    They work well with brackish water.
    They have no pulsation dampers to squash out of shape like my Jabsco diaphram pumps did. Replacement parts are cheap and simple to replace.
    They will happily run from a small motor, model engine DC starter motor (no inverter needed) or anything else you can marry it to. Using a larger driven pulley will reduce output volume, but the pump will still build up pressure.
    They look and sound cool (Kachunka,chunka, chunka....)
    They are cheap if you can get your hands on an old rusty Duro. Change the leathers and valves, paint it blue and brag to your friends!
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    706jim wrote: »
    They look and sound cool (Kachunka,chunka, chunka....)
    They are cheap if you can get your hands on an old rusty Duro. Change the leathers and valves, paint it blue and brag to your friends!

    Hahahaha Your post makes me smile because it's SO true of the old Duros. lol I still have my maternal Grandparent's K255 Duro. it's all rebuilt (new leather piston cups and rubber valves and sitting in my garage, waiting for the day I might need to put it back in service. It supplied all the domestic water for my parents as well and for us kids growing up. Built in the 1950s, it's still ready to go like new. What more could one ever expect of a water pump? What more could anyone ever expect of any home "appliance"???? By the way, once every 15 or 20 years you might have to replace the 4L370 V-belt. Hahahaha
    Here's a video of a rebuilt Duro powered by a 24 volt DC motor that slows down under heavy load. He does have it running roughly 4 times it's designed speed though. It approaches designed speed just before the DC motor stalls. Thing about running it too fast is it will tend to throw crank oil out the shaft and onto the belt. It has no modern oil seal and is designed to allow oil thrown around inside the crankcase by the slinger, to run back to the sump. If it's run too fast the oil doesn't have a chance to drain back, so gets out on the belt. Treat it with respect and rim it at designed speed and it will treat you well for many decades.
    Video here: https://www.youtube.com/watch?featur...&v=smo9dDXysIM
    Here is another Duro video with the pump running at normal speed. this character though has a "little" (his word) 1/2 hp motor on it. The originals came with a 1/6 hp motor, later versions had 1/4 hp, not because the pump heeded more power, but rather that 1/4 hp motors were more common than 1/6 hp and thus cheaper.
    This video: https://www.youtube.com/watch?featur...&v=epL8NBBJdmw
    By the way, I used to run one using a 12 volt generator off an old car. Wired the generator to act as a motor and it worked awesome.
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