For example, if an extra pressure of 5 psi were suddenly applied at the tube valve, the pressure would increase at every point of the tube by exactly this amount. This property of transmitting pressure undiminished is a well established experimental fact, and it is a property possessed by all fluids. The transmission does not occur instantaneously, but at a rate that depends on the speed of sound in the medium and the shape of the container. The shape of the container is important because pressure waves refract and reflect of the walls of the container and this increases the distance and time the pressure waves need to travel. This phenomenon should be familiar to anyone who has experienced the imperfect acoustics of a poorly designed concert hall.
All fluids are compressible.
However, under some range of conditions, it is often possible to make the approximation that a fluid is incompressible. Water, for example, only changes its volume very slightly under extreme pressure. Gases are much more compressible. The compressibility of air, for example, is part of our common experience. If we assume a pump diameter of 1.25 inch, then a force of 18.1 lbf will be required.