2 houses, 2 preasure tanks, 1 pump. Not working Help

I have a mobile home behind my house that we set up a few years ago. We have an artesian well with the pump in the well. The main pump hook up, tank, and preasure switch are in the main house.
We put a t in the line at the well with a shut off valve going to the trailer. At the trailer we have a preasure tank (blatter tank) Every thing has worked fine up untill last winter we shut off the water to the trailer and had it winterized. Recently we were ready to turn it back on and we discovered that the plummer had turned the valve to far and broke the top of the valve off so we could not turn the water on. We dug up the line and replaced the valve. We can get water out to the trailer by turning on a faucett at the house but when our pump shuts off and they call for water at the trailer it does not kick in our pump and they loose there water. I have checked the preasure in both tanks and have set them both at 25 PSI, we have a 30-50 switch.

The only thing I can think of is after we winterized the trailer we had tank failure at the house and had it replaced. The plummer put in a new tank, preasure switch and check valve in the system.

That brings me to my question. Should there be a check valve there at our tank system? I do not remember if there was one there before or not. I beleive that there is a check valve at the well where we teed into the well. Seems to me that if there is a check valve at my house before the switch that would keep the switch from sensing the preasure drop.

If some one has any ideas it would be greatly appreciated.

Thanks

Sounds like you figured it out for yourself. You have a check valve between the tank with the pressure switch and the trailer. Remove all above ground check valves.

Thanks valveman for confirming my thoughts on this.
I removed the valve removed the insides and reinstalled every thing works fine now.