Diaphragm Failure.

[Kaadm]

Hello everyone,

I wonder what can cause the repetitive diaphragm failure within the corrosion inhibitor injection pumps?.

I couldnt find the troubleshooting within the manual and I believe it is intended to meet our process.

Your help will be appreciated guys.

 

[micalbrch]

Wrong diaphragm material? But more likely a problem on the pump's hydraulic side (piston side) or worn valves on the medium side. A bit more information about the pump and a photo of a damaged diaphragm can lead to more precise answers.

 

[Kaadm]

Hello Micalbrch,

Thank you for your cooperation.

PLease find the attached docs the technical data the drawing of the pump head + photos.

Many thanks.

 

[Kaadm]

Sorry here is the technical data.

Regards.

 

[Kaadm]

Also the pumphead drawing is attached here.

Thank you.

 

[micalbrch]

O.k. A PTFE diaphragm. So it is unlikely that the diaphragm is not suitable for the medium to be pumped. Check the discharge side valve balls and seats for wear or blockage first. That's the easiest you can do. The hydraulic side is a bit more complicated due to the small bores and valves. Is the plunger packing tight or is it leaking?

 

[Pumpsonly]

Check the 2 hydraulic compensating and relief valve (item 31 & 32) setting. The valves are suppose to admit the correct amount of oil into the chamber. If the oil inside the displacement chamber is too much, the diaphragm will be pressure against the discharge head (item 2) on every discharge stroke.
Also looking at the data sheet, the max.pressure is 2 x the min.pressure. The internal relief valve would have been set at the high pressure. When the pump is working at low pressure, the diaphragm would be pressed to the end until it is stopped by the discharge head.

 

[Compositepro]

It looks to me that the diaphragm was perforated by too high an oil pressure pushing it into the holes in the head. This pressure is controlled by an internal relief valve in the pump. The diaphragm should not touch the head in normal operation. I think that it should normally be resting against the back support and lifted off only when the plunger pushes some oil forward. A high suction on the inlet to the pump might cause the diaphragm to rest more on the head and get sucked back by the piston, but this would be prone to cavitation and poor metering accuracy. The perforation would still be caused by what I sad before.

 

[Kaadm]

Pumpsonly & Compositepro,

Thanks for your reply.

I would tell you that the failure occur aprox each 6 months for each pump.

I will check the adjustement of the valves within the hydraulich chamber.

What would you think Gents if I will check the torque value(should be 220N.m) for the cover (item 2) bolts as it looks to

me that the diaphragm degree of freedom is limited the tightening value? please correct me if I'm wrong.

I wonder what is the role of the COTTER PIN (item 47) within the system.

Also,How could the stroke adjustement affect the diaphragm?.

Please see the attached document the parts list that may be helpful.

Your help will be appreciated.

 

[micalbrch]

If the failure happened every 6 months, I would assume that the diaphragm lifetime is exceeded for this specific application and pump. If something else was wrong or damaged, why should it take 6 months till the failure occurs again?

 

[Compositepro]

It looks like the cotter pin helps to keep the diaphragm in place during installation of the pump head.

 

[Kaadm]

Micalbrch,

It's okay if something elese were damaged after identifying the cause.

The most common probleme we're facing on this type of pumps is the diaphragm being perforated after 6months aprox and

sometimes less, at the start up of the pump..etc

In the past we had another type of pumps with a stainless steel diaphragm and this problem never occured.

Thanks.

 

[micalbrch]

You are not very precise with your information. So, it is difficult to help you. First the diaphragm failure occurs every six months, now it is sometimes less. You write the failure happens at start up of the pump "etc.". What does "etc." mean? Does the failure not happen always at start-up but sometimes under other circumstances?

The metal diaphragm pump had for sure a much smaller stroke volume. That is a different design. But when you used a metal diaphragm pump in the past, is perhaps temperature a problem? Is the corrosion inhibitor hot?

 

[Kaadm]

The operating temperature is 30°C and the diaphragm is designed to overcome it.

 

[bimr]

Have you run this by the manufacturer?

Your data sheet is lacking the corrosion inhibitor information. What exactly is the fluid that you are pumping.

Have the manufacturer make a recommendation based on the corrosion inhibitor.

Check that the diaphragm that you are presently using is suitable for the corrosion inhibitor.