Air Compressor Pumps.



Like a small internal combustion engine (SIMILAR TO YOUR CAR), a conventional piston compressor has a crankshaft, a connecting rod and piston, a cylinder and a valve head. The crankshaft is driven by either an electric motor or a gas engine. While there are small models that are comprised of just the pump and motor, most compressors have an air tank to hold a quantity of air within a preset pressure range. This compressed air in the tank drives the air tools, and the motor turns on and off automatically to maintain pressure in the tank.

At the top of the cylinder, you’ll find a valve head that holds the inlet and discharge valves. (Don’t worry about knowing which is which, let the experts at H&K PUMP check it out and give you an estimate to either fix it or replace it). Now, as the piston moves down, a vacuum is created above it. This allows outside air at atmospheric pressure to push open the inlet valve and fill the area above the piston. As the piston moves up, the air above it compresses, holds the inlet valve shut and pushes the discharge valve open. The air moves from the discharge port to the tank. With each stroke, more air enters the tank and the pressure rises.

Air Compressor Pumps


Rebuilding an air compressor pump takes a lot of time, a lot of tools, and a lot of parts. To properly break down an air compressor pump and diagnose the problem may take anywhere from 1 to 2 hours of time. A myriad of issues may come to your attention like: the bearings are busted; or the crankshaft front housing seal is leaking; or the piston rods have dug into the crankshaft and won’t move freely. Take a look at the pictures below and decide if you want to try this yourself or if you want the experts at H&K to repair it for you.

Remember, if you decide to try it yourself, here are just a few tools that you will need:

1. impact tools, wrenches and sockets, hammers, lock ring pliers, punches, benches, and screwdrivers

2. an air compressor

3. a vice

4. a press

5. a torch

6. wire

7. a test stand

8. oil

9. pressure tester

10. grease/ lubricant

in total, you should have around $7K – 10K dollars just in tools and equipment in order to disassemble and rebuild your air compressor pump..


The cost to rebuild a pump varies from one machine to another. It typically takes anywhere from 1 to 2 hours to completely break down the machine and determine what the issues are. To do it right, you should remove and replace your bearings; replace all the seals; replace all the gaskets; replace all the rings on both the high and low pressure pistons; replace the valves along with the valve gaskets; hone the cylinders and change out the oil. This process with removing and pressing in the bearings and cleaning up the machine; reattaching all the lines and testing the machine on a test stand can and will take anywhere from 5-8 hours depending on the size and complexity of your pump. The average cost to completely rebuild a 5-10 HP pump is anywhere from $800 – $1,500 dollars and will take between 2-5 business days to rebuild. If done correctly, it should last you for decades to come.