I guess this really applies to boom operators as well.

What do you think about adding 250+ feet of small line (2" or 2.5") to a big boom kit and doing shot-crete?

Bob I can only relate to an experience one of our 52"s had.After a week of shotcreting he had suicidal tendecies.Kinda like slip forming a silo YUK

  Oh you just had to remind me of my slip form experience.  never again.  2 and 1/2 inch slump, air chisels, a big mess.

I have pumped a few with with my old Olin 5-40 ball valve and the nozzleman wanted me to slow down. Not that it was fast it was just to much for them I guess. We had 300 feet of 2.5 layed out. They shot it so dry he was covered in dust.

to much to fast. could get someone hurt . this has been done, but you need to find line pump for safety sake. just my opinion

Can anyone tell me why people continue to do this?

I can only think of one reason; I would like to think that there was some logic somewhere that I just can't see... ;~)

S-Tube line pumps can handle a much wider variety of mixes than ball-valve pumps can. S-Tube pumps with 6" material cylinders and 5" outlets can handle mixes with aggregate all the way up to 1.5" (though typically "big-rock" line pump jobs max out at 1" or 3/4" blend mixes). Of course, S-Tube pumps can easily handle anything that would go through a ball-valve pump - even handling some of the poorly graded pea gravel mixes that tend to give ball-valve pumps problems. AND, S-Tube pumps excel with super stiff shotcrete mixes - which is why most of the world's top wet-mix shotcreters are using S-Tube line pumps.

Ball-valve pumps are great for pumping 1/2" minus mixes in areas like Southern California and Florida where they know how to make a good pumpable line pump mix. But, a lot of places don't make a nice, well-graded pump mix - thus necessitating an S-Tube pump. Also...there are a lot of areas in the U.S. where there just aren't enough 1/2" minus aggregate jobs to keep the pump making money year round. (sidewalks, patios...)

Ball-valve pumps are less expensive than S-Tube pumps (because they are less expensive to manufacture) and are virtually surge free...but, they are really limited by mixes. To me, it's worth the extra expense and the extra surge to be able to buy an S-Tube line pump.

And to call all S-Tube pumps "Shotcrete Pumps" isn't really accurate. S-Tube pumps are by far the world's preferred method of doing wet-mix shotcrete, but they really should just be called "concrete pumps" - most of the boom pump manufacturers today are using the S-Tube.

One last thing...the reason that there is that buildup in those photos is PROBABLY because the pump couldn't pump a stiff-enough mix so they put in calcium so they could pump it wetter and it kicked off faster. (That didn't happen overnight, it PROBABLY happened with 8-10 jobs of not cleaning it (it wasn't a REED, I do know that)). REED pumps have enough pressure to pump very low slump shotcrete mixes without having to add calcium.

The build up in that valve looked to me as if it had taken several days to accumulate. As we all know, once the build up starts it progresses very rapidly.

I keep looking for the logic in purchasing large ball valve machines. I have not found any reason yet to not make an S-tube purchase.

I can not argue about what you said Mr. Reed. I do love my balls though. When I pump I charge as much as booms do. Most of my pumping is slow stuff, finesse types of jobs. I have had this new Olin since January and the other day was the first time I was able to open it up and see what she would do. 8 yards in 12 minutes at half throttle and pump wide open. The man on the end of the hose was happy also, no kick. I do not care if 1/2" minus and grout is all I can pump. If the hose was bigger than 2.5" I would want you to call a boom. We all have become lazy with all the booms doing the work. If a batch plant will work with me on a good slick mix I can do anything. I have pumped 54 yards in 7 hours at a 1" slump for some pool folks. Ball are finicky though. By the way I have a baby Reed for dry shooting, fine machine.