I was wanting to find out, do expect to have some loss of slump during pumping?  If so, how much is typical?

As a rule, yes, there is some slump loss. An inch might be your most typical change. There are many factors that affect this, mix design, obviously, as well as water/cement ratio, pumping pressure, boom configuration, air entrainment.

Thanks for the information.  Is the slump loss due to small amounts of water forced into the pores of the aggregates caused by the pumping pressure? 

Is there any loss of air entrainment as well?

pumpjocky hit the nail on the head,and your right about the air.Another factor is how far of a push on the mud (ie boom + 300').Keep in mind this is hardrock mud,lightweight reacts much differently.

There may be some water loss by absorbtion or adsorbtion into aggregates. (more extreme in lightweight) but most (to my knowledge) is due to water being forced into the cement and/or flyash particles, or other fines. The general thought in air entrainment loss is due to pumping pressure being rapidly lost or even when mud goes into free-fall, creating a vacuum which bursts the microscopic air bubbles.

Along with all the above,Concrete Temperature.Cold out, it will lose the slump slower.Hot out faster.And if you get a late pour in the day.You can even get old mud left over from another job.

I have actually gained slump before...........

I have experianced some crete that loosed a lot of slump on the way. Specialy with some system on it. In the hopper it looked perfect but at the end of the hose we got sausages. Adding gemmicals or water had not much effect. Then I got the angry faces from the finnishers. Like it was my pump that was the cause.

its always the operators fault

does it help to add super to the concrete before pumping?

You mean Super Plastifier? Normaly it helps perfect. But In these particular cases I just talked about we had to ad much more than usual to get it right. And we risked to get a too high slump so the rock would 'sepperate'. Some days you just have to let the customer work for his money ;-) Cant always get it perfect.

Yes, Super Plasticizer does help with pumpability but after about 45 minutes the concrete goes back to its original slump. As far as slump loss, there are many factors, depends on boom size, system, and type of material being pumped. For a typical house slab, don't expect much of a slump loss. But on comercial stuff, you can expect it because there are more ingrediants in commercial concrete depending on jobsite requirements.  2 weeks ago I pumped 2 1/2" slump curb mud through a 39M and 120' of 5" hose. There was no slump loss there. I guess there was no slump to lose. It was like pumping dirt.