ISO tank problem

anyone else haul ISO tanks have an issue with not being able to pressorize the tank? There's no air leaking from the dome, blow off cap or the Chicago fitting, but I can't get the tank past 20 psi and I really need it at 30 to push the product to the storage tank.

I'm thinking the outlet valve is bad, but I honestly can't tell if the internal or external valve is bad.

I've been running compressor at 40 psi since 8 am (it's 4 pm now) and just can't seem to build any pressure.

 

I checked the customers valves and they seem to be open. It going about 20' in 30' up plus 40' 2" hose.

I think air is escaping through the outlet or there's something going on with the customers tank. Seems this has happened before to another driver. Took 9 hours to offload, tank would only build to 12 psi. I'm sitting at 16 psi and can't get it any higher. I still have about 800 gal.

 

I don't remember what the product is, but it did need to be heated above 120°. You may have a point with old product in the pipes.