question

[iceman3000]

Hi to all

Anybody help with a college work question???

What does the term 'bumping clearance' mean and why do we have it??

[Grizzly]

Welcome Iceman 3000.
Usually known as "Bump Clearance"
The distance between the top (Crown) of the Piston and the underside of the Discharge valve plate
( WHICH IN THIS CASE FORMS THE CYLINDER HEAD).

Without some form of clearance there would be physical contact between the piston and the cylinder head.
This also allows for mechanical wear.
Cheers Grizzly

[iceman3000]

cheers grizzly...topman

[Pooh]

However Iceman the distance is critical as too much reduces the efficiency of the compressor due to re-expansion of the gases in the cylinder which can seriously effect the swept volume of the compressor. Typically on a compressor that is set up correctly only about 60% of the cylinder volume is actually pumped through the discharge valve on each upward stroke. the larger the bump clearance the less gas is pumped. This is why screw compressors are more efficient than reciprocating compressors without taking into account the extra frictional losses.

Ian

[US Iceman]

This is why screw compressors are more efficient than reciprocating compressors without taking into account the extra frictional losses.


This effect is minimized on recip.'s when the pressure ratio is lower and increases as the pressure ratio becomes higher.

The screw efficiency is only marginally greater at low to medium pressure ratios.

Recip's are not as bad as they are thought to be by screw salesmen.;)

[frank]

Also known as 'Clearance Volume' in compressor manufacturers data

[frank]

I've moved this post to the correct section.

Iceman3000, please study the different sections before posting any more threads.