To select the pump which will best suit your purposes, you need to know your pressure requirements: How much pressure do you need to generate in order to transfer a volume of fluid from point A to point B? If you choose the wrong type of pump and setup, then you could be left with expensive replacement costs. But while most people understand the concept of pressure, the term “head” or “head pressure” often comes up and confuses the issue.
With this in mind, let's take a look at what head and head pressure are, and how important it is when applied to your pump.
Pressure itself is easy to define. It is a continuous force which is exerted onto an object. But when understanding pressure in a pump system, things are a little more complicated. The purpose of most pumps is to either create a vacuum or to exert pressure on a portion of fluid or air to create what's known as a “pressure differential”. This simply means that there is more force or pressure exerted onto one area than another; a “difference” in pressure. According to the laws of physics, when there is a difference in pressure in a fluid, the fluid will flow from the high pressure areas to the low pressure areas. In essence then, it is the pressure difference which creates the flow of a liquid.
What is Head Pressure?
Head pressure is a specific type of pressure used in pump systems. It is a measurement of the height difference between the fluid being moved and the discharge point. For example, let's say you have a well of water that is 2 metres underground, and you have a tap and pipe system half a metre above ground. The “head” would be the difference between those two points – i.e. 2.5 metres.
But the “head” isn't actually “head pressure”. If head is the vertical measurement between where a fluid is and where you want it to be, then head pressure is simply the amount of pressure you need to get the job done. Read a full explanation of head pressure here.
Other Considerations with Head Pressure
Calculating head pressure can be deceptive. You need to take into account the following:
- Vertical Rise: If you are transporting a liquid from one tank to another, then the liquid level will change. The source will decrease in volume and the discharge tank will increase in volume. This will change the distance needed to pump the fluid. It's important to calculate the maximum possible distance of vertical rise so that your pump will never be caught short.
- Elbows and bends: 90 or 45 degree angled piping adds more head onto your measurement, as fluid moving through this piping requires more force due to pressure loss. Pressure loss from fittings should be calculated.
- Horizontal Distance: The distance a fluid will have to travel horizontally as well as vertically should be taken into account. The greater the distance, the greater the pressure differential required to achieve flow.
- Friction Loss: The amount of friction created by the fluid you are moving, and the materials used in constructing your piping, will create a form of drag, which must be compensated for by increasing the speed of your pump.