Which is the one question to ask?

[bengasman]

There are some people round the north west who talk a great job, know the theory and have got the gab to price up jobs very nicely but then sub them on to the "workhorses" after taking their tidy cut. The usual applies, three quotes (plus one from bg for a laugh) and try to get a recommendation from someone local who has recently had some work done.

2 downsides to this. Cheapest is never the best. Most busy plumbers will put people who ask for quotes lower on the list than those that ask them to do the job. Those plumbers who are not busy this time of year come by and large in 2 groups; not very good, or very expensive.

 

[namsag]

Diyblonde ask all the questions you want from CE30 and guys who have just completed a 6 week course will answer everyone more or less word for word. They wont have a clue what most of it means it and neither will you but you will be impressed.

 

[Onetap]

FFS you lot really are proving the point.

So your saying air entrained water has no effect on NPSH and cavitation then?.

You are proving a point but, I fear, not the one you seem to think.

Entrained air has nothing to do with cavitation.

The difference is that cavitation involves the formation of bubbles of water vapour (or whatever liquid you're pumping) due to the high turbulence, high eddy velocities and low static pressure at the eye of the pump impeller. It involves Bernouilli; the velocity increases so the pressure drops and the liquid effectively boils at the pump inlet.

The difference is that, as the liquid passes the impeller, the static pressure increases and the vapour bubbles implode, ripping particles of bronze (or plastic) out of the impeller. Entrained or dissolved air doesn't do that.


Hemp is used on commercial (mainly) heating systems, some old sweats swear by it.

I said balancing is SIMPLIFIED not eliminated...big difference, the questions are to test the knowledge of the installer something you seem unable to comprehend.

And I say it again; if the heat emitters have large differences in their flow rates and hydraulic resistances, then balancing is not simplified. Balancing is made more difficult to the extent that the system cannot be balanced, despite the presence of commissioning sets with low flow and ultra-low flow double-regulating valves. This was a real installed system which defeated experienced commissioning engineers. The details should have been resolved at the design stage; it was not my design. The 'designer' assumed that reverse return would solve his balancing problems and it did not. The real problem was his lack of understanding of the fundamental fluid mechanics.

I don't do gas and didn't know there were ultrasonic meters. I don't much care, I'm not likely to have any need to get inside a gas meter.

Perhaps instead of offering pathetic criticism and showing your distinct lack of knowledge you would care to offer the OP constructive advice rather than perpetuating the stereotypical plumber/heating installer.

I do not criticize. I simply state facts as I understand them, which differ from your versions.

I don't think the OP is what he/she claims and have no interest in helping him.

 

[namsag]

cavitation is not bubbles of water vapor or whatever is being pumped they are in fact partial vacuums and in effect bubbles of nothing. Check definition of cavitation

 

[Onetap]

cavitation is not bubbles of water vapor or whatever is being pumped they are in fact partial vacuums and in effect bubbles of nothing. Check definition of cavitation

Bubbles of nothing?

This is a lost cause isn't it?

The bubbles are bubbles of vapour that form in the body of the liquid, exactly like boiling. They certainly aren't air bubbles.

How do you get a bubble of nothing to form?

 

[diyblonde]

Onetap: I don't think the OP is what he/she claims and have no interest in helping him

Now I'm confused ... who else would I be and why? I've had cowboys in and now want to make sure it never happens again. And it's "she" by the way.

 

[chrishutt]

who else would I be and why?

You must excuse us, diyblonde, but whenever a poster appears with a name including the word "blonde" we all assume it's some big, hairy bloke from Rotherham trying it on.

 

[namsag]

Onetap As i said do a proper search on what proper cavitation is .
How do cavaties (bubbles ) of nothing form this would be by some strange quirk of physics probably due to high and low pressure zones around impellors /propellors etc.

 

[diyblonde]

Chrishut wrote

You must excuse us, diyblonde, but whenever a poster appears with a name including the word "blonde" we all assume it's some big, hairy bloke from Rotherham trying it on.

Funny but way off base!!!!

 

[diyblonde]

don't know how to do the "quote thing" properly!

 

[chrishutt]

Onetap As i said do a proper search on what proper cavitation is .

You're the one who should do the search, namsag. Onetap is quite right to say that the bubbles are vapour (steam if the liquid is water). A bubble of nothing (a vacuum) could not exist because it would instantly collapse, which is in fact what happens the instant that the vapour condenses back to a liquid as pressure increase.

 

[chrishutt]

don't know how to do the "quote thing" properly!

So you really are blonde!

You click on the quote box to the top right of the post you want to quote from.

 

[NickStone]

don't know how to do the "quote thing" properly!

You phone the guy's mobile (they're rarely on their landline and if you leave a message the good ones are too busy to phone back) and say, 'I need such and such done. Can you give me a quote, please?' Best to get it in some form of writing if you don't know the person. I've found many will send quotes by email now. Ensure the quote includes 'making good' and what that entails. For example, I've just had a new boiler fitted and the making good included cutting and fitting a piece of Bath stone around the external venting, plus re-tiling the inside wall. Someone else submitted a lower quote but said he couldn't make good the Bath stone and couldn't commission the boiler until that had been done - because fumes might have blown back into the property. I accepted the higher quote.

 

[diyblonde]

don't know how to do the "quote thing" properly!

 

[diyblonde]

don't know how to do the "quote thing" properly!

You phone the guy's mobile (they're rarely on their landline and if you leave a message the good ones are too busy to phone back) and say, 'I need such and such done. Can you give me a quote, please?'

Aha worked it out! No I meant to do this type of quote on the forum!!!! Not getting a quote ... but thanks anyway.
God you must think I have the IQ of a feather duster!