Back to Evoqua
Back to Home
Skip Navigation LinksEvoqua Water Technologies > en > Brands > Envirex > How to prevent your chain and scraper from crashing

How to prevent your chain and scraper from crashing

By Doug Pimlott, June 6, 2016

​Without proper maintenance, your chain and scraper system can cause some serious problems or even crash. At Evoqua, we have serviced hundreds of chain and scrapers over the years. Below are three simple tips to keep your chain and scraper system running smoothly.

Please Note - prior to conducting any in tank maintenance, please make sure your tank is drained, proper lock out tag out procedures are followed and all state and local OSHA safety practices are followed.

1. TEst YOUR carry Chain Tension

Carry Chain tension is paramount to avoid the chain “skipping" a sprocket tooth or worse, falling off the sprocket and ending up in “spaghetti junction” with the chain and flights wrapped around the shafting.  Chain tension should be checked annually to prevent these problems.

Chain tension can be easily measured by having a ~160 lb person stand on the chain in between two flights on the ground. The chain should not touch the ground with this weight. If it does, then links need to be removed.  It is important to perform this test during the coolest part of the day. Thermal expansion is prevalent in non-metallic applications, and in the hot sun on a summer day the chain will naturally become slack when the tank is drained.

To adjust tension use a chain fall or “come-along” of 2,000 Ibs (908 kg) maximum capacity and heavy-duty straps looped around the chain barrels (do not use metal chain or cable). Make all adjustments at the tank’s floor level and approximately midway between the effluent and influent ends of the tank. Remove all visible slack from all sections of the chain, excluding the catenary. Remember to remove the same number of links from each strand and to keep the flight attachments opposite one another.

​2. Check Shear Pin Alignment

 Shear pins are a simple and inexpensive tool that are the last line of defense for your drive unit. They are also the item that is most often neglected or missed.

When inspecting chain and scraper systems, we often find shear pins out of alignment - where the neck is not centered with the split line in the shear pin sprocket. This causes the pin to shear at the thinnest point, instead of at the full diameter, which compromises the performance and safety of your system.

Another common issue is when the pin has been replaced with a bolt. This should absolutely not be done, as it will effectively disable the safety of your drive. Envirex shear pins from Evoqua are the exact length of the bore of the sprocket, flush on both ends to ensure effective performance and safety.  If you are experience nuisance tripping of your drive, contact your Evoqua representative.

​3. check Wear Strip spacing

Wear Shoes and wear strips are designed to absorb the friction of the unit when it touches the tank floor or return rails. They have an excellent coefficient of friction and can last many years, even in high grit applications.  However, wear shoes and strips inevitably need to be replaced and the placing of wear strips is critical to chain and scraper system performance.

When installing polymeric wear strips, all strips should be positioned and spaced per the drawings before attempting to field drill and install the anchors.  Once the strips are positioned, locate and drill the holes for the anchors in the center of the countersunk hole or slot in the wear strips. This will allow maximum expansion of the strip and prevent curling or overlapping if the tank is drained and thermal expansion takes place. 

There should be a gap in between the strips in the ambient temperature condition.  Gap measurement depends on the type of wear strip, so refer to your Operation and Maintenance (O&M) Manual for the correct spacing. If you are unsure or do not have your O&M manual, please contact your Evoqua representative for assistance. 

​Evoqua has over 100 years of experience in chain and scrapers through Envirex® and other OEM brands. Feel free to contact us with any of your chain and scraper questions.

Find out more information about our Aftermarket Services