I've been recently having a problem with product setting up in a small section of boom pipe. I run a 32m schwing and I've been having a problem with about an inch to an inch and a half of product setting up in the tunnel tube that passes through the boom. I've never had this problem before and it happens pretty frequently now. 

The company I operate with now I am a mixer driver and an operator and with my previous employer I was primarily an operator. The reason I mention that is because with this employer the pump does alot of sitting between jobs. Also, my company is a small outfit so I do a lot of small, sometimes slow-moving projects. Also because we are small, I do a lot of waiting between trucks. I try to keep the product moving or circulating as much as possible while keeping it cool as well. 

I've always cleaned out the same way and have never had this problem until recently. I'd have to say at least 50% of the times I prime out I'm tearing the elbows and tube out of the joint between sections 2 and 3 and find that there is a layer of concrete set up between both 90s and in the short straight tube. 

Sorry for the long explanation but I need some advice here. 

How are you washing out ? Sponge I assume

Yes. I've always used the soft ones but recently switched to the harder ones to try to help this problem but it still happens. 

https://www.youtube.com/watch?v=NyYrtNsQQlI

make sure rubbers are new and greased ,

Are you sucking sponge back from 5" elbow ?

If so and still getting build up -sounds like sponge is getting stuck and then building enough suction to break free, but in doing so the sponge comes back too fast and sliding by gravel and cream. Find out where catching ,probably new pipe or elbow with lip. If you go water, sponge then water again and another sponge you are guaranteed to have clean pipes. My two cents.

Thanks I'll try 2 sponges one hard one soft next few jobs and see how that works out. I've always used one soft and never had this problem before. By the way there is about 90% new pipe on the boom. I thought about maybe being a lip.