what is "doming out"?

i never heard of that term, but some vac tanks have a device (float) that will shut off the vacuum when the liquid level rises too high.

 

Vacuums have a structure inside the dome lid where the vacuum is pulled on the tank. It suspends a hollow Stainless Steel ball which floats up and blocks off the vacuum to keep from sucking liquid back into the vacuum pump. I don't think the vacuum pump would like to swallow liquid.

Often the vacuum line comes down to a 'catch can' that can be drained incase some foam or liquid gets past the ball check.

 

With gasolinr tanks you have a overfill sensor up on the inside of the dome and when the product closes that you've "domed" out. It shuts all loading down on your lane. Then you need to reset the scully system after you've drain some product off before you can continue to load. It's all part of the scully system for overfill protection. It may be different on other trucks but that's the type I always used.

I've seen some drivers have a bad system and blow product at full speed out through bad dome gaskets and piping all over the truck. A few hundred gallons of gasoline was spilled but on the loading rack it's easy to clean up. Glad it wasn't me thou.

 

Wis Bang is EXACTLY correct, I couldn't have said it any better myself, that's why you have scrubber tanks to catch the water that does go into your suction hose, some trucks have isolation valves to act as a check valve between the tank and the pump also.

For the record, when you suck up your ball and lose suction that is not a bad thing, it just means your at maximum capacity. Depending on if you have an air line ran to your valve on the back of your truck to air out your hoses or not you may want to watch your sight glasses and when your just about full close your valve on the frac tank or manifold and unhook the cams on the camlock and work your hose around in the connection on the tank or manifold (it wont come completely out because its under suction, it just allows it to suck air and clean your line out for you). One thing to keep in mind is, if your line is full of water or flowback your not going to want to spill it and if there is no entrance for air at the end of the hose it will not suck, it needs air to create vaccum so thats why alot of swedges (the fitting with the threads that threads into a frac tank valve) have a ball valve on them, so you can close the valve and suck the line dry by sucking air through your ball valve.


Feel free to ask me anything about hauling water and I will do my best to give you the straightest answer possible to keep yourself out of trouble and make your experience hauling water a good one.

 

Speaking from my limited experience back in the 1970s, (yeah I'm old), sucking water into the scrubber was usually the "kiss of death" for a vacuum pump. Generally not right at the moment, but if you can imagine flooding the insides of a hot compressor with cool water, the pistons, valves, etc, trying to work against the water instead of air; add that to the fact that many vacuum trailers are hauling lease water (unfiltered salt water) from a well site.

IIRC, the old time trailers we used had two scrubbers, one inside, one outside, and were not foolproof; water in the outside scrubber meant water got in the pump. I'm sure today's systems are greatly improved, and probably not so critical, but the scrubbers were there as insurance, not as a signal that you were loaded.

 

you ever hear of a "thompson unit" ? one of the first vac units i was ever exposed to was one of those. it probably new in about 1976, 5000 gallon carbon steel tank, with deutz? diesel and vac/compressor mounted on front end. and yes there was at least one time when the liquid went past the scrubbers/float ball and went in the vac pump. i recall the oil turned foamy/milky. needed oil change and service when that happened.

 

Not much water gets into either scrubber tank, its usually mixed with oil, I'm talking like maybe a couple cup fulls if its not drained out daily and the pumps not flushed daily which it should be.

I never said the scrubber tanks have anything to do with being fully loaded, they are there to protect your pump as you said.

 

Gashauler was right. Back in the day (before 1980) gas was loaded from the top on tankers, they had no shut off if you overfill, so when you were dumping 500 gpm of gas and it reached the top it made a "dome" of gas coming out of the fill hole. BTW Gashauler, the 3 arm diesel lane at Kinder Morgan in Vegas is the stuff of legend (7 minutes to load 7400 gal. **jealous**...