The pump to select?
The pump to select? How to determine the pump to select? The correct pump. (exit at any time by scrolling to end of this document) A centrifugal pump performance curve is simply a tool which enables anyone to literally see how a pump will perform in terms of HEAD and FLOW. Every pump will be capable of developing a specific PRESSURE (PSI or BAR measurement translated into feet or meters head) at a specific FLOW (normally represented in gallons per minute or liters per minute) A note on establishing flow. If you do not know the flow you require it is relatively simple to determine if you just take it one step at a time and add all the outlets together. For industrial applications, for washing, heating or cooling the equipment will have a flow and pressure on the design plate. Flow in a system can be established by understanding the requirements. In our example we will use a house which has two bathrooms, a dishwasher, a washing machine, an electric geyser in the roof and a guest toilet with hand basin. Also a sink in the kitchen and an outside shower for the pool area. So we have the following outlets :- Bathroom hand basin taps 4 Bath taps 4 Shower taps 6 Toilet cistern 3 Guest basin tap 2 Sink in kitchen 2 Washing machine 1 Dishwasher 1 TOTAL 23 If we assume each tap will be required to deliver 2 gallons per minute (GPM) at 44 PSI or 3 bar, then we simply need to determine how many outlets we would expect to operate at any one time. It is unlikely that all toilets, all showers, all baths etc will be on at the same time. A good method is to take a third of the total outlets as your flow need for any single moment in time. In our example that represents 23 divided by 3 or 7.6 make it 8 outlets. This means a flow requirement of 8 X 2 = 16 GPM or 60 liters per minute. A note on the concept of PUMP HEAD. Think about the highest point of your body, the top of your HEAD. It is the same idea with pump language, Head refers to the measurement in feet or meters from the center line of the pump (the pump shaft center line) to the highest point to which the unit is expected to deliver fluid) The above definition of head is limited to what is known as the Static head. in other words, this is the measurement of the vertical height which should never change, it is static. Lets say you are needing to deliver water from a tank at the bottom of your garden, to the geyser at the top of your roof. The garden has a steep bank from the house to the lower area where the tank is located. The house is a double story. If one measures the height from the base of the tank […]
Pump pressure control system
Pump pressure control system The simple pump pressure control system available from Pedrollo, South Africa has many advantages. We often have the request to assist with the design on systems where water is pumped from a dam. river. pond/ bulk storage to a service tank next to a home etc. The problem seems to occur when the user becomes embroiled in working on complicated control systems and ends up with horrific costs for cable runs or radio telemetry systems. The simplest system to use is to have the pump fitted with either an electronic pressure/flow controller like the Pedrollo Easy Press or a Hyrdrosphere/pressure switch system. Pedrollo Easypress This controller activates if it recognises a flow demand and / or a pressure set point. The really great feature of the Pedrollo Easy Press is that it has a storage vessel to buffer the pressure on/off switch. This buffer zone is fantastic for two purposes, potential dry run operation (lack of water on the suction side of the pump like an empty dam or low water level in the source) and long discharge pipe lengths. This buffer is essential to enable the unit to switch positively and not to instantly switch when the contacts would close and open with oscillating flow. Once one has a pump fitted with an automatic controller the rest is relatively simple. A ball float valve or a solenoid valve at the point of delivery completes the cycle. Basically the pump reacts to the line pressure. In this case the ball float valve in the receiving tank rises and closes the valve, pressure in the line builds and flow slows. As the flow stops with the closed valve condition, the controller (which is located at the pump and can be up to 200 meters away from the pump) stops the pump. Water usage from the tank will drop the water level, the ball float drops with the water level, opening the valve, releasing pressure and generating flow. The controller sees the resultant flow and pressure drop and the pump starts. We do like to use the older technology HYDROSPHERE PRESSURE PUMP systems in long er pipe runs. The size of the hydrosphere must be linked to the pump flow at the operational head of the system. We like this system for very long pipe runs up to a few Km due to the added protection provided to the motor for stop/start conditions. The hydrosphere tends to absorb and delay stopping and starting due to pressure and flow variations in longer pipe runs, small leaks, air entrainment etc. One does need to ensure that the pumps are protected with the correct overload protection. We like to recommend a proper control panel be installed with the pump which includes surge protection. In Southern Africa with power cuts, brown and black outs which can be frequent, it is crucial to ensure the electrical components are adequately protected. The above represents the simplest way of controlling a pump remotely without using […]