I need to make a one way valve that would allow water or other fluid one way but if there is too much pressure on the opposite side the valve will close and stop water from flowing backward. Can anyone help?
R V parts stores have an item which allows a garden hose to be connected to the RV but the tank water inside the RV is not allowed to come out of the RV and enter the water hose (supply) so only fresh water comes in, nothing goes out.
You are looking for whats called an RP or back flow device. These may be sold at home depot. However, I know your local plumbing supply house would carry them.
Its called a check valve.
It's called a Check-valve. Easier to buy than build. They are made in brass and PVC.
We need to know what exactly the work/purpose your 'one way valve' has to perform. You have given overall description that got you fairly good answers here. But if you really want to solve a problem by yourself (instead of going to any plumber) then you have to understand that the one way valve used for garden drainage system is different than the swimming pool drainage system and numerous other household applications one can think of where 'one way valve that would allow water or other fluid one way but if there is too much pressure on the opposite side the valve will close and stop water from flowing backward'. Let me assume that you are in a place where neither plumber nor the hardware shop is readily available. In that event you may consider placing one ‘flap-valve' on top of the outlet pipe. The valve is simple metallic piece may be from tin, iron, plastic etc., that can withstand the force applied by water/liquid on it. The flap-valve would have to be hinged hanging from top part of the drain/pipe in a way that it can move away with the pressure of the inside tank or reservoir and then would shut-off when reverse flow (RF) would occur, by the force created by the RF. If you have seen any Tube Well or DWT Pump then you may notice that these are also having a RF (Check Valve) mounted either at the bottom of the sunk-pipe or somewhere in-between. This help in having the flow of ground water upward only and any reverse flow back to the ground is automatically restricted as the 'flap' would fall onto the pipe orifice due to gravitational weight as well as weight of water column on top of it. Hope this would help learn the basics.
