Can't control Cavitation

[peterako]

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]

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 Sparks]

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/34cleare...er132perf.aspx

[peterako]

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]

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.a...rom=Thumbnails

[russ]

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]

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.]

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

[SCharles]

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]

Suction is a dirty word in the pumping game.