It's basic hydro...
In order to push water thru the filter, the upstream side pressure has to be higher than the downstream side. If the filter clogs, it needs a bigger pressure if you want any significant amount of water to pass thru.
- Upstream of the pump is gravity fed. Let's say you have a really deep fresh water tank (2ft deep) and it's full to the brim and the filter is flush with the bottom...2ft of head will generate about 0.9psi. So the theoretical max pressure differential across the filter is 0.9psi..though in reality it will be less as you won't be able to drop it to 0.0psi if there is water flowing and most tanks are not always full nor are they 2ft deep.
- On the downstream side of the pump, the pumps generally put out pressure somewhere on the order of 30-50psi...that's a lot more pressure available to push water thru the filter while still retaining enough pressure to send the water to the various outlets.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV