Cavitation?

[Dannyparty92]

Hi all would someone please be able to explain what cavitation means in regards to heating pumps. How does cavitation occur and how would you prevent/fix it?

 

[Plum Bob 66]

Check out wizegeek.com, type in cavitation in relation to hot water systems best explanation ive ever read to date.

 

[Dannyparty92]

thank you plumb bob

 

[TomLane]

Sounds painful, be careful what you click on when searching for this on Google, might get more than you bargained for!:sweatdrop::tongue3:

 

[Dotty]

Cavitation occurs in liquid when bubbles form and implode in pump systems or around propellers. Pumps put liquid under pressure, but if the pressure of the substance drops or its temperature increases, it begins to vaporize, just like boiling water. Yet in such a small, sensitive system, the bubbles can't escape so they implode, causing physical damage to parts of the pump or propellor.
A combination of temperature and pressure constraints will result in cavitation in any system. No manufacturer or industrial technician wants to run pumps that keep getting affected by cavitation, as it will permanently damage the chambers of the device. The vaporization actually causes a loud, rocky noise because the bubbles are imploding and making the liquid move faster than the speed of sound!

(Thanks PlumBob!)

 

[Guest123]

Wow John, I'm impressed!

 

[Dotty]

Wow John, I'm impressed!

Not just a pretty face you know! :rofl:

 

[Deleted member 25704]

Hi all would someone please be able to explain what cavitation means in regards to heating pumps.

1. How does cavitation occur

2. How would you prevent/fix it?

I will do my best here to put some practical meaning to the science that croppie explained so well:

1. What I can do is add some meaning to this in terms of heating systems and pumps. If we consider a central heating pump on an open system, it creates +ve pressure on the outlet, and -ve pressure on the inlet. Now, if the heating system is in say a bungalow (low static head) a 'sub-atmospheric' situation may arise on the inlet side of the pump.

In addition if the pump speed is high or pump oversized, and the boiler thermostat is faulty, or set on high, then water may start to turn to vapour on the inlet side of the pump because of the combination of high circulating temperature and sub-atmospheric pressure (note if you increase the pressure in a water system the boiling point of water is raised [e.g. at 3 bar = boiling point of water 136 degrees centigrade], if you lower the water pressure to sub-atmospheric then you boiling point of water is reduced to below 100 degrees centigrade). Hence vapour is sometimes produced on the inlet to the pump, in low-head situations. However, the feed and expansion pipe creates a neutral point, which continually equalises the pressure near to the inlet of the pump, creating the potential for cavitation described by croppie.

2. To prevent cativation on pumps make sure they are fitted in accordance with manufacturer, on the flow and after the cold feed and vent. For low head situations fit a myson air-jec which helps. Make sure circulating temperature is not too high, usually 82 degrees centigrade or lower for condensing boilers. For bungalows never fit pumps in loft, and make sure there is adequate head above pump position, usually at least 1m - if less fit an air-jec.

Note: For shower pumps the same science is transferable - keep hot water storage temps low, avoid pumps that over-run supply creating negative or sub-atmospheric situations that lead to cavitation. Try to install pumps with a good static head above them.

 

[Leo21]

Cavitation occurs in liquid when bubbles form and implode in pump systems or around propellers. Pumps put liquid under pressure, but if the pressure of the substance drops or its temperature increases, it begins to vaporize, just like boiling water. Yet in such a small, sensitive system, the bubbles can't escape so they implode, causing physical damage to parts of the pump or propellor.
A combination of temperature and pressure constraints will result in cavitation in any system. No manufacturer or industrial technician wants to run pumps that keep getting affected by cavitation, as it will permanently damage the chambers of the device. The vaporization actually causes a loud, rocky noise because the bubbles are imploding and making the liquid move faster than the speed of sound!

(Thanks PlumBob!)

The good old copy and paste.

 

[Dotty]

I neither admitted nor denied the fact!

But I did apportion acknowledgement to Plumbob accordingly!

 

[REDSAW]

'bubbles darling'

makes more sense when he's had a few.lol

 

[Leo21]

I neither admitted nor denyed the fact!

But I did apportion acknowledgement to Plumbob accordingly!

Blimey have you been taking legal advise or was that written by your legal representative?

 

[Dotty]

I happen to be very well educated.

I also drink, a lot, which explains the usual gibberish you get from me!

 

[Dannyparty92]

Thank you very much clanger that has cleared things up for me alot.

 

[Plum Bob 66]

I neither admitted nor denied the fact!

But I did apportion acknowledgement to Plumbob accordingly!

Many thanks kind Sir!

 

[acecharly]

Thank you very much clanger that has cleared things up for me alot.

Id imagine cavitation could solve alot off issues just dont tell ya mates what your into lol