I found a thread on here from 2009 about dry packing on a boom pump. My like pump is dry packing after about 8 strokes. I've changed just about everything ... plates, cutting ring and kidney seal. Had hydro pump pressure checked, new fluid, new rings and seals on rams. Tried pumping from two different concrete companies. Not using a special mix, regular 3000 psi big rock. I want to say I've ruled out everything on my pump and it is the mix, but I've pumped this mix a lot with no problems. Anyone have a suggestion? 

Are you in an area where you have crushed rock sand or natural sand?

In VA it's pretty common to have 50/50 natural/manufactured sand.  Sometimes the ratio gets a little off track if the RM company needs to save some on a tight job.  

Cement/ash ratio at 80/20 or straight cement? 

If you can, put the line size and mix specs on here and I am sure some of the guys can fix you right up with a way to make it pumpable.

Also, may try going up a size in hose and see if that gets it through if that's an option.

I have had this same issue with all crushed sand and 2.5 inch line.  Jump to 3 inch line pumped like butter with same mix.  Changed to blended sand, pumped like butter.

Also might could try backing your RPMs down to around 1000-1200 and ease it through.  Less Rpms creates less friction, and doesn't force as much moisture in

Hey Joel, I'm in New Orleans. We have natural sand from the Pearl River. I'm reading up on batch mixes again and am going to hang out with a dispatcher friend to learn what their plant is mixing. Also, I am going to try a 4000 psi pea gravel through my 3" hose and see how that works. It would suck if I did all this work and it is the mix !!!

Trying not to forget about all of you pumper new and old, I take it you are using a swing tube line pump,i bet if you would smaller rock and a 3500 mix 3000 psi is weak i never pumped anything less than a 4000 psi 1/2 in rock plus I used Bentonite with a wad of wet newspaper in from, I used Bentonite for the hole time i owned my company,never had much trouble unless someone got in my way like my son he always want to prime out about and 8 in slump and guess what we plugged dam near everytime , I would prime out on a 5 in slump never had a problem,then i would wet it up and pump dam kids. 

Do you mean it's dry packing before you get primed? I used to try priming with some of the official pump primers for a long time and it would dry pack/ rock pack 9 out of 10 times. I've switched to .5 gal betonite per 4.5 gallons water with a sponge in front of it and now I have no problems.

Hey BC, last test I primed and got 10 pumps. then dry packed in my 4 to 3 reducer twice. I also just received some sample packs from Fritzpak that I am hoping to use. They have an additive I can add directly to the truck drum to "smooth out" 4 to 5 yards of concrete.  I have been priming with Superlube 100, a bottle to a 5 gal bucket poured into the first hose. 

Maybe ask some other operators in your area of you know any. I once replaced my hydraulic cartridges after the ready mix company told me no one else was having any trouble. Guess what there wasn't anything wrong with them 

Mix up 80 lbs of masonry mix and dump it in the reducer or first hose. Its a lot of work but will work. Slik  doesn't work it segregates the concrete.

So after you plugged twice it went fine after that? The only times I've really dry packed in the reducer is if you get something in there that just partially blocks the reducer, Are you sure you're getting your valve clean after each pour? I would consider running 2 grates if you don't already.

By big rock do you mean 3/4"? I would try going 3500 or 4000 with 3/4" rock instead of pea gravel, Pea gravel can be really miserable if your batch plant doesn't know what they're doing. 

I wouldn't keep throwing money at your pump unless stuff is obviously wore out on it, Especially if it's just on the prime. 

Man if you are trying to pump 1" aggregate through 3" system in this area I believe you will continue to have issues . I think you are rock packing then dry packing behind it , I do believe 3/4 " is the max aggregate we allow for 3" line , preferably 5/8" , but I have never heard of anyone in this area of having that size aggregate , so we only pump pea gravel through 3" , but instead of a 7 sack mix , we can pump a 5 1/2 sack mix. 

That's where I'm at right now. Going to try a rich mix and see if it will go thru. I was going to change more parts but my order got delayed so I cancelled it. I've done a lot to it already. Now I have to see if anyone is pumping in the rain! LOL

You say you only pack on the prime? Thats no reason to change any parts is it??  The problem is elsewere.. 

What happened to me some times: Worn out reducer but new hoses. That will cause an edge of a few mm which will block the rock and by that cause a drypack..

have the plant blend 3/8 and 3/4 rock. if the sand is too clean it will push the water out, we lost the fine blend sand and fly ash but still have slag. hey the pump does not lie when the mix is too rough.

Good idea on the reducers I would measure your reducer and see how worn it is