Pump won't drain sac.......

I just bought 2 launchpad big sac 800lb sacs and a sumo pump. This weekend we went out and decided we were going to see how much of a difference it made. Where we were is really shallow so in best interest of the saftey of the prop I decided they needed drained. The first bag was filled pretty full (spewed water when I capped it after filling) and drained without a hitch. The second bag however would not drain and it didn't spew water when I capped it after filling. The pump would run but no matter what we did it wouldn't pump water. Is there something wrong with the pump or the valve on the sac or am I doing something wrong?

May be a stupid question, but did you push the pump down into the bag? If the pump is on top of the bag and the bag is not full of water, then the pump will not prime because it is not in contact with the water inside the bag. If the other bag was full, then the pump may have been able to prime itself.

+2. Seems like the only logical outcome is the pump wasnt priming bc it wasnt touching the water.

^ That's probably what it is. Those punps can be real finnicky. I'm sure you did push it into the bag and move it around quite a bit but it still didn't prime and start pumping right? You have to turn the pump on and off to get it to start pumping. If it doesn't prime right away it usually won't start pumping unless you turn it back off then back on.

Some pumps aren't self priming either - so if it is/was sucking air you'll have to turn it off, jam it down, then start again...

like other said, my guess is that is wasn't getting the water

I did push it down etc but didn't turn it on and off. Thanks!