Diaphragm Pumps – Premature Diaphragm Failure
Diaphragm Pumps have become very popular during the past few years, especially as standard equipment in Air Blast and smaller High Pressure sprayers.
They are, of course, more modern and have many advantages over the traditional piston pumps, especially because the liquids being pumped never come into contact with the pump’s working parts. (In piston, plunger and roller pumps, the upper working parts are generally lubricated by the liquids being pumped, and the bearings and seals are always in contact with those chemicals).
However there is an aspect about diaphragm pumps that the user is generally not aware of, and certainly, in most cases, not mentioned by the manufacturers of the diaphragms in these pumps. Diaphragm pumps are designed to be pushed, not pulled. When they pressurize the liquids, they are being thrust by a piston and are properly seated on the head of the piston for that purpose. Thus, they are fully supported and therefore do not stretch, pull, deform or suffer any other stress that they were not designed for.
When the piston ends its stroke, it pulls the diaphragm as it goes back into the lower part of the cylinder, creating a slight vacuum in the pressure chamber that draws new liquid into the head, which will then be pushed out to the discharge hoses by the diaphragm. when it is pushed again by the piston.
As long as the inlet lines from the tank are not clogged, the filter is clean, and the shut-off valve in the line feeding the pump is open, there is no problem. The diaphragm pulling the liquid into the chamber is not stressed.
However, if there are obstructions in the line of any kind, the diaphragm has to pull hard to fill the chamber, creating what is called a high vacuum. This now causes the diaphragm to be pulled by the piston head, deforming the center mounting of the diaphragm.
If the pulling effect becomes extreme due to a higher degree of clogging, and, of course, a higher inlet vacuum, then the diaphragm will be severely deformed and even be scoured by the edge of the washer holding it to the head of the piston. Inevitably, the washer will cut the diaphragm, and you will have the subsequent mixing of oil and water. And that means diaphragm failure.
The best prevention for this problem:
- Keep filters clean
- Wash the screens out thoroughly after each application
Also, check your inlet flow periodically for blockage. Do this by disconnecting the inlet line from the pump and observing the flow. If the liquid (and please. do this with clean water so you don’t inadvertently dump chemicals) flow is normal, no problem. If you get a trickle or little more, and not what you would consider normal. Then you have got some blockage either in the line or plumbing.
Chemicals, especially wettable powders and coppers have a habit of cakeing-up in the fittings and sprayer lines. Also look for rags and other foreign objects as these also have a habit of ending up in drains and pipes. As a last resort: call your friendly RotoRooter man!
Another common cause of the high vacuum problem is shut-off valves in the inlet lines that are closed when the sprayer is started. Diaphragm pumps will pump air when there is no liquid around, so if your inlet line is closed, they will sit and suck vacuum with the subsequent consequences.
If you take simple precautions and periodically check and clean out your inlet lines, you will find that your diaphragms will last much longer than you expected and you will not only be satisfied with your pump’s performance, but save time and money as well.
If you are spraying intensively (every two weeks or so), make sure you replace the diaphragms and do a full maintenance job on your pump annually.
