Grease Pump

I HAVE A ONE MORE DOUBT SIR LARGE PISTON IS THERE IN PUMP AND WHERE IS THE SMALLER PISTON WE HAVE ONLY PLUNGER IN GREASE INJECTORS

Please avoid all-caps.

Without a picture of your grease pump, I can only guess that your "plunger" serves the function of my "small piston." My first reply was an abstract idea, which might be implemented in various ways.

A related concept is "hydraulic intensifier" (or "amplifier"). These terms can be Googled.

Check Hydraulic Press Principle of operation.

8 bar into a piston of area 22cm² produces a Force of ~ 8kg/cm²*22cm²=176kgf

Now if the exit orifice is 1cm² then the pressure is ~ 176kg/cm² (or~ bar to simplify) (~2500 PSI)

Sorry to have to push the point, but "Now if the exit orifice is 1cm² then the pressure is ~ 176kg/cm² (or~ bar to simplify) (~2500 PSI)" is simply not true.

If 8 bar goes into the system at one end, then 8 bar appears at the other end.

If, as in your worked example "8 bar into a piston of area 22cm² produces a Force of ~ 8kg/cm²*22cm²=176kgf", then the same pressure applied to an exit orifice of 1 cm² will produce a force of only 176/22 = 8kgf. It is the resultant force which is proportional to piston area. The pressure does not change from one end of the hydraulic system to the other. If it did, the fluid would flow due to the pressure difference.

Sorry, not so. If you put 8 bar of pressure down a hydraulic line what comes out the other end is still only 8 bar of pressure. Now if you are thinking about the force at one end against the force at the other end, that's different. If the piston at the start end has twice the surface area of the piston at the other end, what comes out is half the force over twice the distance (the reverse of the garage jack situation).

Here is a diagram of a pneumatic pump.

This is used to pump a hot melt butyl. The cylinder or motor at the top strokes the smaller cylinder or pump at the bottom. The force of 8 bar is multiplied by the area of the large cylinder transmitted thru the connecting rod to the area of the smaller cylinder.

Here is the trick:

The grease is collected in a reservoir and kept under pressure, only to let it slide down or to the place where a grease pump plunger can pump up the grease.

In big industrial systems think of a tank where the plunger works on the bottom.

If a lot of grease i in the tank it will sink down by gravity. If not, it can be helped by pressure, e.g. air pressure well or not separated from the grease by a piston or membrane.

The grease pump has 2 valves, often spring loaded ball valves that operate in a seat.

The channel in the pump is e.g one square inch and the valves deal with this. The motion is operated with a plunger- rod.

If this rod is driven by a pneumatic piston, say of 10 square inches, you have theoretically multiplied the pressure by 10.

With a piston of 100 square inches you multiply by 100.

This is a simple explanation, maybe not explained simply.

Hope it helps.

Think "ThumbTack".

The Centromatic pump is an air-operated, single stroke, grease pump.

Some Centromatic pumps uses compressed air for forward stroke and for return stroke.
Other Centromatic pumps uses compressed air for forward stroke only, and springpower for return stroke.

The pump dispenses grease on forward stroke only (single stroke working pump).
(Double stroke pumps dispenses grease on both strokes)
On return stroke, the plunger chamber is filled up with grease (reservoir with spring-loaded follower).

The piston rod in the air-section is connected to the plunger rod in the fluid-section.

The ratio between air-piston section and grease-piston section (plunger rod) is approx. 21/1 .
(1 bar on air-side results in approx. 21 bar on grease-side)

Best rgds,

John Sijs