pneumatic tank

I've no experience with a set of tanks, but I've plenty of experience with pneumatic tanks.

Is your lid gasket leaking? That will do it every time.

Tank cracked anywhere? You may not even notice a leak, sometimes they're very difficult to find.

And sometimes, that's just how they are. I know mine drops pressure when I open the product valve, but it recovers fairly quickly, especially when I'm hauling a coarse product like pebble lime.

How much time are you losing through all this?

 

There's a leak somewhere. I was having problems the past couple weeks with one trailer, tank pressure would stabilize, then start dropping steadily over 5-10 minutes. Found the blowdown valve wasn't sealing properly.

If your second tank isn't having issues, then it's something on the first tank that's leaking.

 

Does it do this on all the pods, or just on number one?

I suspect you may have a leaking check valve in between your line valve and #1 hopper tee.

 

If it starts with the product valve open, the seal inside could be torn. Spray soapy liquid on it when open.

The other ideas here sound good as well.

 

There’s always some slight air leak on these trailers. Unless it’s a significant leak, it wouldn’t cause your problem, IMO.

You might have a half clogged valve. Have you opened the bottom to see if there’s a rock, or any build up? Does the lever rotate easily? If there’s a sticking sensation anywhere on the movement, you likely have some buildup or a rock chunk in there.

Also, when it finally starts going empty, does the pressure drop slowly? If so, you may need to replace the rubber flappers (the blue toilet plunger looking things).
I just had all the innerds on my number 1 pod replaced because of this.