under older Schwing 52, late 80s i been told.  great pump, can be rough boom, watch out when the tip section pipe fills with a 4inch hose.  suspended slab 5th floor, two section verticle.

we stop the pump for 1min - 10min, up close or streched out,  we start the pump, fill hose give er a couple stokes to fill the pipe and off we go.  every time id get a couple air shots on stroke 11 - 13, id guess thats hopper.  know it not low hopper cause i dont feel it in the hose.

any thoughts /experience with this?

Even is the hopper was empty by stroke 11 mixer shuld have caught up by them. I run a 43 and around  6 strokes gets me from hopper to the tip so I'm thinkin 8-9 shuld get ya on a 52. What is the slump? If ur pouring stiff n u have a week vibrator u may be caching air due to cylinder not totaling fliling.

It's the concrete between concrete that slides down the boom and stopping in elbows or level pipe. if you are not aware of this you will have a hose whip and hurt someone. tnis is a common problem with big booms. you must pay attention to boom configuration when stopping and watch how much concrete drains from hose also don't set hose in mud to stop spatter it will cause plug and hose whipping.

I have seen the back pressure from the weight of the material in the two vertical sections push on the delivering ram while shut down and forcing the ram to bleed back and inturn give the brain a false signal that it is in reverse causing an empty lung to double-shift one cycle before correcting itself after one complete cycle. This can happen on the older 52m and burp out the end at about 11 strokes. it would be less strokes on the newer,  bigger pump kits but about 11 on them old big sticks of yesteryear.

thank you for the input.