We manufacture a pump in China. The reason we have it done in China is to provide an actual profit margin. We started manufacturing it in the US, but it reached the point where it just cost too much, it was either fold up the company or outsource to China.
We opted for outsourcing the pumps to China.
We’ve been having the strangest problem concerning the lip seal we use to seal our pump motor shaft. It is a standard 1/8 inch cross section x ¼ inch ID x ½ inch OD lip seal. After we started manufacturing the pumps in china we began having substantially more warranty returns due to leaky pumps.
It took a long time, but we finally realized that occasionally the seal would spin inside the plastic gland it is contained within. It turned out that for 10 years we had been using the wrong cross-section type of seal, which was symmetrical. Now the factory is telling us we shouldn’t use that type of seal for a rotary shaft application. It would have been nice if they had mentioned it 10 years ago when they helped us choose a seal.
And it worked so well for 10 years! Thinking back on it, we now know why we had some mysterious leaks even back then. There were a whole host of changes we made when we switched to the Chinese manufacturing, but we still used the same motor shaft sealing technique and seal.
To solve the spinning problem the Chinese manufacturer had some custom seals molded, but when he did the life-testing, the seals were only lasting from a couple of minutes to an hour or so. Wee need a 500 hour life or better.
We spent weeks trying to figure out why the seals only seemed to last for a few minutes to a few hours when the Chinese manufacturer did life testing on them. Our life testing of the US seals we had been using was getting life expectancies of about 500 hours, unless they spun of course.
We could not figure out why the Chinese tests were so poor… let’s say catastrophic, Same motor and pump, same stainless steel shaft, same plastic pump housing, same water pressure and temperature. We decided it had to be the material the Chinese were using.
We found a compounder here in the US who would custom make us the rubber material, Nitrile, with the properties we needed for our pump. The minimum order cost us about $1,000 but we got enough material to make about 80,000 pumps. The seals are pretty small after all.
It took about a month to get the compounder to furnish us the batch of nitrile and we shipped a small portion off to China for them to mold into lip seals.
Again the Chinese life testing resulted in seals only lasting minutes. We investigated the curing times and molding method the Chinese factory was using and tried changing those parameters. Same result.
I was getting quite frustrated. The Chinese were blaming “abrasion” for the problem. I told them to send me some samples of the new seal including one of the “failed” seals. When the seals arrived and I found the “failed” seal I was a bit puzzled. I could not tell the difference between the new seals and the failed seal. It looked brand new.
I installed the failed seal in a new pump and began life testing the pump. After about 200 hours of running I took the pump apart and checked the seal. It showed significant wear as would be expected, but inner lip still had more than half the original thickness. There were no leaks.
To be continued…
