A pressure sensing device is disclosed for use in a connecting structure foranextracorporeal blood treatment machine. The device is adapted for having aliquid flowing there through and for sensing the pressure of the liquid. Thedevicehas a first chamber into which the liquid flows from a first opening at alower partthereof to a second opening at a top part thereof. The device has a firstorifice forthe liquid into/out of the device, which orifice is placed at the upper partof thedevice at a higher level than the second opening. A first channel isconnectingthe first orifice with the first opening. A second orifice for the liquid outof/into thedevice is placed at the lower part of the device at a lower level than thefirstopening. A second channel is connecting the second opening with the secondorifice.
