A wash-down cylinder was leaking every two weeks. The cylinder was 63 mm bore, 300 mm stroke, on a food-processing conveyor. It was a standard NFPA cylinder with Buna-N seals. The customer used 80°C water and caustic cleaner to wash down the machine twice a day. The rod seal kept failing. The wiper was fine. The rod looked fine (stainless 304). The Buna-N seals swelled. They turned soft. They leaked in a week.
Buna-N (nitrile) is fine for hydraulic oil. It is not fine for caustic at 80°C. The chemical attacked the elastomer. The seal swelled by 30%. It no longer fit the groove. It squeezed out. The customer was buying Buna-N seals because that’s what the cylinder came with. They didn’t know the seal material mattered.
We replaced the seals with EPDM. EPDM handles hot water and caustic. It doesn’t swell. The cylinder ran for 18 months without a seal replacement. We also added a stainless steel rod wiper (POM) to keep the caustic off the seal. The rod was already 304 stainless, but we switched the tube to 316 for better corrosion resistance in the wash-down environment. The total cost was about $80 in seals and $40 for the wiper. The customer had been spending $30 per seal kit every two weeks — $780 a year. The fix paid for itself in two months.
If your cylinder is in a wash-down or chemical environment, the seal material is the first thing to check. Buna-N is for oil. EPDM is for water/steam/caustic. FKM (Viton) is for chemicals and high heat. Don’t use the default seals because they’re cheap. Use the right material for the fluid it sees. A $20 EPDM seal beats a $30 Buna-N seal that fails every two weeks.
