what is Bumping clearance ? How to check it , how to adjust and what is its significance ?

it is very important to maintain for compressor otherwise there is change in the clearance volume and affects efficiency of air compressor. It not only affects the volume ,if it less then, compressor valve, cylinder head and piston get damaged. So, it is very important for engineers to keep its adequate for proper working of compressor.

Bumping clearance measurements procedure

What is Bumping Clearance ?

Bumping clearance is defines as , space or clearance available between the cyl. head of the compressor and the top of the piston when piston is at TDC.

It is also known as clearance volume. This is very very important for the compressor, lesser the clearance volume more improvement in volumetric efficiency.

This clearance is left in the compressor has some significant. This is required for the purpose of preventing bump of piston on cylinder head. On new compressor, it is adjusted by the manufactures. but with time, compressor need overhauling and here difficulty start.

The clearance volume should be neither too small nor too large. Furthermore, it has an impact on the efficiency of the machinery and should be checked at regular intervals. Clearance volume change when the compressor head open and gasket of correct thickness is not used. or, the cylinder tightened over , in that conditions clearance decrease due to squeezing of gasket. Many engineers face the problems in adjustment of bumping clearance during fitting cylinder head back and cause differ in efficiency of compressor.

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How bumping clearance change with time ?

when the compressor is constructed in factory, its clearance set by the manufactures. But this clearance not always fixed through out the working. During working due tp some factors, it get changes. what are the factors which affect the change in clearance.

1.Change of size of cylinder gasket

with time we need to overhaul the compressor. We also need tp open cylinder head according to pms running hours. Opening up of cylinder head affect clearance. how opening of head affects ?

In certain types of Compressor, valve need to be overhauled and change then we need to open cylinder head. Cylinder head open and at fixing back , we need gasket of proper size. if it is not used of adequate size, it change the clearance of compressor. If we used gasket of more thickness then clearance volume increase. or, if we use gasket of same size but overtighten then clearance get decrease.

2.Wear of the main bearings of compressor

Engines have some running hours. wear down of main bearings cause lowering of the crankshaft and finally, piston get lower and increase in the clearance.

Due to not proper lubrications of wearing, wear down of main bearing also occur.

3.Wear at crank pin wearing

Bottom connecting rod bearing is known as crank pin bearings.

with time or due to not proper lubrication, wear down occur of crankpin bearings. Due to wear down of crank pin bearings, piston moves up and clearance get decrease. This cause piston hit the cylinder head.

This wear can be easily known. when our compressor give a impact sounds during running at unloaded conditions in starting pr stopping.

The wear of crank pin bearing also get by slow decrease in the pressure of oil overtime.

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What is the significance of Bumping Clearance ?

If bumping clearance increase

it causes decrease in the volumetric efficiency. hence, compressor take more time to fill the air bottle.

If bumping clearance decrease

There is a chance of damage of hitting of cylinder head due to piston., especially in the compressor running in unloaded conditions during start and stop.

Note :- engineers always play safe so, they give few millimeters of extra clearance volume.

How to check bumping clearance of compressor ?

Bumping clearance of air compressor

Engineers should must know the answer of this questions. This question frequently asked in Mrol in class 4 exam. Let us know how to check it.

the following methods are used for the measuring clearance volume ?

1.Using feeler gauge

If suitable opening is available then the piston is moved on top by rotating flywheel. Put feeler gauge from opening and clearance checked 2, 3 points.

2. Lead wire method

This is the most used method for measuring the Clearance volume.

Take a lead from store and make a small ball according to clearance of the compressor. Open the Valve and put it on two or three places on top of piston.

Note :- putting lead wire from cylinder head opening.

Now turn the flywheel slowly with tommy bar, Make at least two rounds. after that remove the lead wire and measures its thickness by using micrometer or calipers. The measurements of lead wire give clearance.

Note : – during taking clearance with lead wire method, we do not include the clearance due to wear down of crank pin or main bearings.

What is the correct method of taking bumping clearance ?

Air compressor bumping clearance

as i have already told you that taking clearance by using lead wire method, not include clearance due to wear down of crank pin and main bearing.

To take exact clearance , turn the piston at TDC and the connecting rod is jammed with the help of a Crow bar.

How to adjust bumping clearance ?

If you take the bumping clearance by above method and found clearance is incorrect the, need to adjust. But how to adjust it. These are the following methods to adjust.

  1. Put the thin shims b/w bottom end bearings and foot of the co. rod of the compressor. Thus clearance is adjusted.

After adjusting , you must take the bumping clearance again to ensure that it is in acceptable limit.

This is all about Bumping clearance of Main air compressor. If you have any doubts related to this topic, do not forget to comment. If you like content please share it with friends.

Bumping clearance

People also ask

Why small clearance is required?

As possible small clearance required to increase the volumetric efficiency of the compressor. Otherwise need more time to fill the air bottle. But keeping in mind that small clearance with acceptable limit otherwise damage to the cylinder head of the compressor.


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