venturi

[johnwkey]

Daft question but which is the "venturi", I had a venturi Carb on a Cortina a couple of decades ago, but I dont think thats it!

 

[ChrisR]

It isn't just a flue or fan fault, half a dozen possibilities, which you'll be able to diagnose with a manual and a meter. If you can't do that, have to suggest you wouldn't be able to fix it.
The poor hot water is a separate fault; probably diaphragm, sludge or sensor.

 

[Gasguru]

johnwkey

The venturi on a boiler works exactly the same as a venturi in a carb.

Named after Mr Venturi the device is used to detect a flow of gas or liquid - they are frequently used in boilers eg to detect fan operation and water flow and just as with carbs they can block.

 

[Agile]

If you want all the calculation formula then they are here:-

http://www.efunda.com/formulae/fluids/venturi_flowmeter.cfm

Boilers use them as flow measuring devices to confirm exhaust fan operation in conjunction with a pressure sensor.

Tony

 

[ChrisR]

Odd that they say at that link that the formula is for incompressible fluid then give an example with air!

 

[Agile]

I think that they are thinking about air movement where a low pressure difference across the venturi will cause minimal changes in density in the air at atmospheric pressures.

They do mention the increase in temperature when its pressurised but I thought they then reached the wrong conclusion as to the effect. Maybe they muddled up Boyle and Charles?

Tony

 

[chrishutt]

For those that are interested in how Venturis work and the principles behind it, this might be a useful link. You can alter the shape of the tube to observe changes in pressure and velocity.

 

[ChrisR]

HEY MOD
what happened here - this started off as a thread about an Alpha...??

 

[Agile]

Even Alphas have venturies and an understanding of the principles of their operation is essential to an understanding of boilers including Alphas.

I have this feeling that a boiler venturi is designed to be non linear, that is to give little output until the fan flow is say 90% of maximum. Does anyone know if this is the case or not?

Tony