Can't control Cavitation

Bigwooo
Bigwooo Solar Expert Posts: 62 ✭✭
I'm off grid and my water is brought by truck. I'm drawing from a 10,000 gallon underground storage cistern using a 12v Dankoff flowlight booster pump to charge the pressure tank. My head is 5 feet in a full tank and nearly 9 feet when the tank is low. I'm using a 10" inline filter on the suction side as required by the manufacturer. I'm drawing through about 5' of 1 1/4 inch pipe and 4' of 1 inch pipe (1" pipe was installed through the foundation instead of the 1 1/4" I specified).

I'm getting cavitation bubbles in my water filter chamber that are being drawn into the pump. I've double checked the foot valve to see if it was causing problems, I even removed it to see if it was causing an obstruction. With nothing obstructing the pipe it is still cavitatating. The lower the water level, the worse the cavitation becomes.

I've triple checked for air leaks on the suction side, and I'm confident there are none.

My question is:

Am I drawing water beyond the pumps capacity?

Would the dankoff 30" filter be more efficient than the 10" and cause less friction and reduce or eliminate cavitation?

Or... is the head from the pump to the water level just too much, and should I consider switching to a submersible pump?

Thanks for the input.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Can't control Cavitation

    Head? Typically, that is a positive number (pushing against 9' of head)--But in your case, it sounds like you are drawing/lifting water 9' to the pump?

    Anything you can do to reduce the inlet restrictions would be a help.
    1. Use a screen rather than a "filter" on the pump inlet? Put the filter (if needed) on the pump outlet.
    2. Can you plumb the pump down closer to the water level--The siphon effect may help keep pressure at the pump. If you put the pump below the water line, it could siphon the tank dry if there is a leak/break somewhere (make sure that water goes someplace safe instead of flooding your basement/battery bank for example).
    3. Can you put a fitting near the base of the tank and fixture up the pump there (pit beside tank? Again--pits can flood, so drain/sump pump/acceptance that you may need a new pump if pit is flooded for some reason).
    4. May need another type of pump with better suction capabilities.
    From the data sheet:
    Suction Capacity

    Low speed model 20 vertical feet (6 m) standard model 10 Feet
    (3 m) at sea level – subtract 1 ft. for every 1,000 ft. altitude (1 m
    for every 1,000 m). Note: Suction capacity may be further limited
    by intake pipe friction.

    Excessive suction causes cavitation (vapor bubbles) creating
    noise and excessive wear. Intake piping should be 1” or larger.
    Pump should be mounted as close to the water source as possible.

    Choice of Capacity
    • Standard Model for highest flow
    • Low speed model (DC only) has higher pressure capacity, and
    is best when:
    • Suction lift greater than 10 feet
    • Intake pipe smaller than 1” size
    • Extra-quiet operation is desirable
    Which pump model do you use?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Bigwooo
    Bigwooo Solar Expert Posts: 62 ✭✭
    Re: Can't control Cavitation

    Bill, thanks for the suggestions.

    Yes I'm drawing 9 feet on a low tank, and 5' in a full tank.

    I can only lower the pump a maximum of about 18" due to the design of the utility room where the pump is located, I'm not sure it that will make much of a difference.

    Without additional construction, there's no way to put the pump in a pit.

    Yes, I may have to get a better pump (although I thought this was), so far it's been a pain. I have a backup surflow 2088 pump that I'm going to try if I can't solve the cavitation problem.

    Right now I'm using the standard model pump and have built my system within their suggested parameters.

    I think you make a good point.. I'll try replacing the filter with a screen. The mfgr. is insistent on using the the filter on the suction side, but my water is clean, and there is little chance of introducing contaminants so a screen should be just fine.

    If I have to replace the pump (the Surflow will be good for now, but as I expand, I'll need a higher GPM pump than the surflow), does anyone prefer submersible or a different surface pumps?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Can't control Cavitation

    "Better" is a loaded word... ;)

    A pump that is better at the application may be a "better" use of the term. Boost pumps would not normally be designed to draw much suction at the inlet.

    It sounds like you have the "high speed" pump--and 10' (less 1' per 1,000 feet of elevation) is the maximum recommended lift. Dropping the pump 18" would probably help. Also checking to make sure you don't have any air leaks in the piping to the pump too (i.e., air leak in filter canister).

    The low speed is supposed to lift 20'--and that is about the best you could expect from any pump.

    If you have lots of close 90 degree (sharp) bends, that could hurt too... Next time you address the plumbing, they may have "long" 90 degree fittings, or put two 45 degree fittings together--that can reduce pumping losses quite a bit too.

    Submersible wise--I know that it can be difficult to get a good one that won't fail after a year or three... You could get a "simple" low cost/pressure submersible pump and use it to provide positive pressure to your boost pump instead of a high pressure/high power submersible. Just wire the submersible to come on every time your boost pump is activated.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Can't control Cavitation

    Check for restrictions on the output of the pump too; they can cause pumps to 'churn' water and aerate it.

    There's something vaguely familiar about this scenario which I can't quite bring to mind just now. If it surfaces from the murky depths of memory I'll let you know.

    Oh, and 'head' is a measure of the height of water 'behind' a pump, so it would be the higher number when the tank is full and lower as it empties.

    Edit: What is your shut off pressure set at? I have a vague notion of that fitting into the formula somewhere (trying to jog my own memory).
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: Can't control Cavitation

    I have the 2920 115 vac booster pump and had cavitation problems after changing the 10"filter. What happened was the filter (and the next one as well) were not fitting properly in the housing allowing very small particles of dirt/rust to get past the filter point and block the emergency screen. The emergency screen is on the intake pipe barb/thread connection into the pump head. It's a pain, but I cut the nylon line, spin off the nylon barb fitting and tap out the crud...this solves the problem.

    I just have to take the time to put the filter in properly and all is well. I'd forgotten about the screen until I was prompted by the Dankoff teck people, and it's on the label on the motor housing.

    So my advice is check that the filter is not clogged and is fitted properly and then take things apart down to the pump head and clean out the emergency screen...it is like an envelope stuffed down inside the nylon threaded/barb fitting.

    Good Luck
    Ralph
  • Bigwooo
    Bigwooo Solar Expert Posts: 62 ✭✭
    Re: Can't control Cavitation

    Well...I've checked the screen and it's clear, I tried to re-seat the filter again, no luck.

    I think I'll try lowering the pump as much as I can and see if that helps. If that doesn't work. I'll try eliminating the filter and put in a screen. If that doesn't work, I'm in the market for a new pump :grr

    Thank you for the input everyone.
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Can't control Cavitation

    İt is unusual to place a fine screen on a pump inlet - asking for problems. A big trash screen maybe but not a fine screen.

    Filters are for downstream of the pump where you have pressure to work with.
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    Re: Can't control Cavitation
    russ wrote: »
    İt is unusual to place a fine screen on a pump inlet - asking for problems. A big trash screen maybe but not a fine screen.

    Filters are for downstream of the pump where you have pressure to work with.

    It may be unusual but it is a normal practice for systems that cannot be allowed to fail. It is a strategy in high reliability situations (a boat at sea, water systems (both kinds) on the International Space Station. It only works if someone is there to change the screen if the filter ahead of it fails. In diesil engines Perkins use to do this on an air filteration screen hidden in the manifold to protect against the main filter tearing a hole in itself and passing all the trapped stuff into the engine.

    It is usually cheaper (piece of mind) to just have a spare pump but...
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Can't control Cavitation

    A boat at sea has a trash screen (as large of a mesh as possible)- not a fine mesh screen. The mesh size is normally determined by how large of a particle the pump can safely pass.

    Really it goes against everything İ ever learned about pumps to restrict the suction more than absolutely required. İ am talking about 95% of the pumps in the world İ suppose - process pumps for industry.

    İf there has to be a screen (filter) in the suction it should be as oversize as is practical - meaning whatever mesh size is required but a very large screen area. Smaller is not better!
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    Re: Can't control Cavitation

    Russ,

    You would want the screen to protect the pump if the input filter were to fail in certain applicattions. Shurflo has application where a 20 mesh filter is used in two places to protect their pumps. Smaller is better because it alerts the user that something is wrong!

    It all gets back to what your philosphy is on a failure. You design from the general to the specific. One size never fits all !
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Can't control Cavitation

    İ pointed out that the inlet screen is normally sized to protect the pump only - it would be totally wrong to have the final system filter on a pump inlet - unless one is looking for problems. İt is too easy to have a filter system at the outlet.

    Rather a flimsy pump if it requires a 20 mesh screen at the inlet. İ have never seen a backup (2nd) screen on the inlet.

    All this makes it too easy to burn up a pump.

    İ agree that İ look at these things from an industrial perspective where you do every thing possible to prevent problems.

    To me, if the pump can't handle fine particles then it is the wrong piece of equipment.
  • Bigwooo
    Bigwooo Solar Expert Posts: 62 ✭✭
    Re: Can't control Cavitation

    The Dankoff pump manual emphatically states that you need the filter on the inlet side to protect the pump from damage. Well...today I removed the filter cartridge (the one the mfgr. recommends) and the pump is purring like a kitten. No cavitation at all. I tried to suck air through the filter and it was difficult, I can't imagine the difficulty the pump is having drawing water through it.

    I think I'm going to bypass the filter and install a course screen to keep any big stuff out. My suction pipe inlet is about 5 inches off the bottom of the tank, and my tank/water are pretty clean. I think it would be very difficult to suck something into the pump. If I do, and the pump fails, then I'll use my backup surflow until I can get a less finicky, higher volume pump.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Can't control Cavitation

    Wet filters often have a lot of surface tension in them (try to get air out of a wet 600 thread pillow case) but maybe the filter was too "fine" ? inlet to a pump should really be as un-restricted as possible, and you just strain the lumps out.
    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 ||
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  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: Can't control Cavitation

    The simple thing to try, and it sounds like you are going to, is just remove the filter and see if the problem is still there. If it goes away, you know the filter is restricting too much and you need to somehow reduce that. If it is still there, at least you know it's not the filter.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • Bigwooo
    Bigwooo Solar Expert Posts: 62 ✭✭
    Re: Can't control Cavitation
    Brock wrote: »
    The simple thing to try, and it sounds like you are going to, is just remove the filter and see if the problem is still there. If it goes away, you know the filter is restricting too much and you need to somehow reduce that. If it is still there, at least you know it's not the filter.

    Thanks everyone for the suggestions. The problem is definitely the filter cartridge. I took the cartridge out of the canister and fired it up with an empty canister. Runs fine, no cavitation bubbles. I'll either eliminate it, or see if I can find a filter that's not so restrictive.
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: Can't control Cavitation

    You're brave, but if your water source is really clean nothing to worry about. Usually you can find different grades of the same size/brand of filter, perhaps that will solve the problem. If not, how about some quick release fittings so you can remove the inlet screen fitting and clean it out in seconds instead of minutes...? I considered this as a fallback to having the filter properly seated if that was my problem. Something like cam type connectors for trash pumps...only tiny.

    My pump is below the source water level unless the tank is nearly dry...no lift whatsoever, lift would increase problems and decrease performance no doubt.

    Ralph
  • peterako
    peterako Solar Expert Posts: 144 ✭✭
    Re: Can't control Cavitation

    I agree with Russ , i also use a screen on inlet to protect the pump inlet and after that i filter the water.
    On this way you also protect the water supply from parts out of the pump :roll:

    Yes i had a failing pump ( i have a spare installed always ) before failing totaly or leaking i found parts from the seal in my filter.:D

    P.s. any restiction on the section is bad for a pump and a lost energy.

    Greetings from Greece
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    Re: Can't control Cavitation
    peterako wrote: »
    I agree with Russ , i also use a screen on inlet to protect the pump inlet and after that i filter the water.
    On this way you also protect the water supply from parts out of the pump :roll:

    Yes i had a failing pump ( i have a spare installed always ) before failing totaly or leaking i found parts from the seal in my filter.:D

    P.s. any restiction on the section is bad for a pump and a lost energy.

    Greetings from Greece

    Only if you are trying to pump more water than the inlet is capable of for it's size or restriction from the filter. If you are gravity fed this is pretty hard to screw up short of basic maintenance.

    A clogged filter will cause what the OP's problem was. Now suppose that filter was to break and dump it's contents into the pump? Suppose the OP who lives down on the Baja had sand in that filter? Places like the Baja are reasons to use a polyester based inlet filter into a stainless based "doomsday filter" and finally into the pumps inlet. You can watch the current into the pump and tell when it is restricted or, just do the maintenance....
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Can't control Cavitation

    Rule number 1 for any pump installation - İnlet restrictions must be held to a minimum.

    İ realize this blog is mainly aimed at residential installations where all sorts of funny things are done but good practice is good practice. Putting fine mesh on a pump inlet is not good practice.

    İt is not hard to find the correct pump for a given service but most people don't realize what they are getting in to and things can easily go down hill.
  • peterako
    peterako Solar Expert Posts: 144 ✭✭
    Re: Can't control Cavitation

    i keep a KISS ( Keep It Stupid Simple) rule for my installation.
    That because i am away from my home for long periods so my wife must be capble to see the problem.
    in my setup if the filter is dirt the flow out of the water tap drops so my wife can easly see the filter if it is not dirty but the pump is running whit low pressure i told here to plug out the main pump and plug in the spare pump. all mechnical connected only the electrical plug must be changed.

    A pressure switch is protecting the pump and yes i have a current moitoring on the pump. but as a engineer i avoid any filter or restriction for any pump.

    Greetings from Greece
  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Can't control Cavitation
    Bigwooo wrote: »
    Thanks everyone for the suggestions. The problem is definitely the filter cartridge. I took the cartridge out of the canister and fired it up with an empty canister. Runs fine, no cavitation bubbles. I'll either eliminate it, or see if I can find a filter that's not so restrictive.

    From my experience with DI pumping systems at work lots of these problems are caused by small leaks on the inlet side sucking air into the system. Replace/clean all the o-rings/seals. I like to have a short section of clear pipe on the pump inlet to check for a bubble stream.
    http://www.clearpvcpipe.com/clearsightglasses.aspx
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    Re: Can't control Cavitation

    And I would use one of these if the situation required. As Dave Packard (from HP) once said quality is just conformance to requirments. Anything more and you should be charging for an option. Anything less is not acceptable.

    http://www.clearpvcpipe.com/34cleareastarandregepdmsocthrbasketstrainer132perf.aspx
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • peterako
    peterako Solar Expert Posts: 144 ✭✭
    Re: Can't control Cavitation

    I agree that most of the time it comes from smoll air leaks, special after the pressure drop from a filter. but a screen using the correct size avoids pressure drop.
    Cavitation is a number one killer for a pump. I see a lot off pump problems on ships based on cavitation.
    Keep in mind that a filter pressure drop is enough to allow air to by pass a baering seal after use, that is not the seal fault it must seal against pressure not under pressure (vacuum)

    greeings from greece;)
  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Can't control Cavitation
    peterako wrote: »
    I agree that most of the time it comes from smoll air leaks, special after the pressure drop from a filter. but a screen using the correct size avoids pressure drop.
    Cavitation is a number one killer for a pump. I see a lot off pump problems on ships based on cavitation.
    Keep in mind that a filter pressure drop is enough to allow air to by pass a baering seal after use, that is not the seal fault it must seal against pressure not under pressure (vacuum)

    greeings from greece;)

    The shaft seal should be behind the discharge outlet (pressurized) so it almost all-ways just leaks when it goes bad.

    One of our pump types at work. http://www.pricepump.com/cen_pumps.asp?model=MS&from=Thumbnails
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Can't control Cavitation

    Pressure rating: 100 psi @ 70º F, non-shock

    These filters are designed for the discharge side of the pump - as is normal.

    Just protect the pump with minimal filtering on the inlet.
  • SCharles
    SCharles Solar Expert Posts: 123 ✭✭
    Re: Can't control Cavitation

    I'm reviving this old thread because I have the same problem as the OP and wonder whether he or anyone has new info'. I've been running my Dankoff booster pump for at least 20 yr. and did not realize there was a cavitation problem until it got worse in conjunction with a small air leak I had develop. Dankoff [or Conergy or whoever they are now] advised me to install the clear tube kit [inlet and outlet hoses] to see whether I could find air bubbles flowing in the intake, and I did and found the bubbles of air. After days of hassling with the system, I got the idea to remove the filter from the inline filter housing and, what do you know, zero bubbles. I have the filter placed on the inlet line, as Windy Dankoff insisted way back in the 80s when I bought the pump and which the co. still insists is necessary to protect this pump. They [and he] recommend 5 micron filtration, though I was using 10 micron due to my inability to locate a 5 micron element last time I bought them.

    I have the low speed version. Water level is only about 3-4 feet below pump.

    The thing is, with the filter element removed, the pump virtually hums. Very quiet. And it brings the pressure up to cut-off more quickly now. All these years, apparently I've had cavitation as the noise level has always been fairly high, and I never suspected anything as back when I was looking at pumps, all info' warned that Dankoff pumps did make a lot of noise.

    I am presently running the pump without the inline filter element installed as I wait for a call back from the pump mftr., which can take a while. Anyone have any updated info' about this problem??...there must be thousands of these pumps in use.

    By the way, to answer someone else's question, yes, the very fine screen DOES GO in the INLET port of the pump and the filtering DOES go in the inlet side of the system. These pumps last a long time; I installed mine back in the late 80s and it's been in use since then, no problems except this cavitation thing. I did replace the motor brushes a year ago, and the old ones still had some life but I went ahead and did it while I was going through the system to replace a check valve and some general maintenance. So as far as the pump goes, it is a really good piece of equipment.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Can't control Cavitation

    For background information--A nice article about off-grid water systems.

    So, my questions...
    • Can you filter the water coming into the tank (output filter on well/creek pump). Filters in pressurized output is much better.
    • Can you install a floating water pickup (1/2 way down the page) (keep inlet above base of tank). Let sand/dirt settle and floating pickup in "clear water".
    • Install a very large / high flow filter on the pump inlet. Larger filters should have less pressure drop at low flow rates of smaller pumps.
    • Can you "dig a hole" and place the pump father below the water level in the tank--Increased inlet static pressure will help reduce cavitation. (note, pump in pit can get flooded--need water alarm / drain to protect pump if rain water gets in pit/leak in plumbing/pump).
    • If your water does not have much grit/dirt (clean source, tank settles, etc.)--Then the pump may be subjected to more wear from cavitation (collapsing cavitation bubbles can cause very severe erosion inside the pump) may be worst than the wear from the filtered materials.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SCharles
    SCharles Solar Expert Posts: 123 ✭✭
    Re: Can't control Cavitation

    You can do any of those, I suppose. However, for the Dankoff pump, filtration and fine screening are supposed to be at or prior to the inlet port of the pump. I spoke at length with Windy Dankoff when I bought mine from him back in the late 80s. In fact, I drove from Colorado down to his place in N.M. to pick it up as I was going anyway to buy from him some big phone co. batteries back then. He showed me the pump and how to set it all up. He was adamant that strict filtration was needed, prior to the pump, because the pump could be damaged or worse by any particulate matter. In fact, he set me up with a 10-micron-screen-protected foot valve for the intake line, an inline-filter housing with a 5 micron filter element, plus the very fine screen which is designed to drop into the inlet port of the pump. The current owners/makers of the pumps say the same thing, I spoke with them last month about my cavitation problem and am hoping to speak with them again in a day or so. The pumps are, or so I'm told, built to such fine tolerances that any "grit" or contamination will cause rapid and premature wear of the pump.

    I don't know anyone else around here using a Dankoff, and that is all I've ever had for house system pressurization, so that's all I know about. Whether all that pre-pump filtration is really necessary, I cannot say. I have gone by what I was told when I bought the pump.
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Can't control Cavitation

    Suction is a dirty word in the pumping game.
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: Can't control Cavitation

    Dirt is a dirty-er word in a Dankoff pump :D

    Ralph