Low pressure is generally considered to be anything under 0.5bar, Medium Pressure 0.5bar and High Pressure 1.0bar and over.
If you have a high pressure system then you can use any tap, if you have a medium or low pressure system you will need to ensure that the tap you are buying will work on a pressure that low.
Not all our taps are suitable for medium or low pressure systems but they do have a minimum working pressure figure on each one. You just need to ensure that this number is at least as high as your system or higher.