WorldWide Drilling Resource

71 DECEMBER 2021 WorldWide Drilling Resource® RENEW - SUBSCRIBE NOW! Understanding Head for Pump Specification Adapted from Information by Publitek Put simply, head is the height at which a pump can raise up, and is measured in meters or feet. It is used when specifying centrifugal pumps because their pumping characteristics tend to be independent of the fluid’s specific gravity, often referred to as relative density. Avoid confusion: head vs pressure - Head can sometimes be confused with pressure because there is a close relationship between the two parameters; but there is one fundamental difference. Head is fluid independent, that is, regardless of the fluid’s relative density, the pump will lift it to the same height. Therefore, it does not matter whether the fluid is water or heavy sludge. Pressure, on the other hand, is fluid dependent and is affected by gravity. Therefore, the same head will generate a different pressure depending on the fluid’s relative density. Suction levels - Suction conditions are also relevant to the pump head. If the suction level is lower, the head measured will be less, and vice versa. The pump’s motor converts electrical energy into mechanical energy, which the pump then imparts into the fluid as pressure. Raising or lowering the suction level therefore adjusts the potential pressure of the liquid. The more pressure the pump delivers, the higher the head will be. Total head - Because pump manufacturers cannot know the suction level parameters, they calculate the pump’s total head (Figure 1). To do this, they subtract the total suction head, which is measured as height above sea level, from the total discharge head. The next important consideration is how much friction needs to be taken into account. Friction loss depends on the length and size of the pipework, bends, and gate valves, through which the fluid flows. The sum of the head and friction loss will give total head. Total head is a more reliable indicator of pump performance than pressure because it indicates what the pump can do regardless of the suction conditions. The total head combined with your flow requirement will allow you to choose the right pump. Pump performance - The performance of the pump at a certain speed (RPM) can be found in the manufacturer’s datasheet displayed as the flow rate (Q) versus head curve. At the maximum head, the pump has zero or little flow. This is often referred to as the shutoff head. When looking for a pump, ensure that the head provides a sufficient flow rate. For example, if you require the pump to operate at 780 gal lons per minute, the maximum head would be 86 feet. This selection procedure only applies to centrifugal pumps. For piston pumps, which can provide more pressure, they are selected based on flow only. The units for flow rate are U.S. gallons per minute (USgpm) in North America. However, in countries using the metric system, the units can vary; litre per minute (l/min), metre cubed per hour (m³/h), and litre per second (l/s). So, be sure to check your units during the selection process. The total head parameter is crucial when buying or renting the right pump for your application. It gives an accurate indication of the pump’s performance, regardless of other contributing factors such as suction level and fluid density. Figure 1: Friction losses are affected by length and size of pipework, bends, gate valves, strainer, and velocity of flow. WTR New & Used Tricones PDCs Drag & Claw Bits Drill Collars Bit Tipping Subs & Stabilizers HDD Bits & Reamers DTH Hammer & Bits Custom Fabrication Junk Mills / Fishing Tools Rod Henderson 661-201-6259 Eran Henderson 661-330-0790 Send your comments on this issue of WorldWide Drilling Resource® to