Air operated double diaphragm pumps (AODDP) require the correct amount of air pressure (PSI, pounds per square inch) and air flow (CFM, cubic feet per minute) to deliver the proper amount of fluid. A typical air operated diaphragm curve shows how the correct amount of pressure and CFM are required to deliver a required flow rate against a discharge head.
In many Air Operated Diaphragm Pump applications, the end user has ample amount of pressure on the gauge reading but has no idea the available CFM. It is just as critical to have the correct amount of CFM available as it is pressure to achieve a desired flow rate. Many end users might state that they have a 100-psi gauge reading on their double diaphragm pump but they are not getting the desired 'litres per minute' (LPM) as promised in the flow curve.
In this situation, remember that the pressure to the pump is needed to achieve the desired flow point but the CFM determines the actual output in LPM. The pressure to the pump overcomes the discharge head, and the CFM determines the actual gallons pumped per minute.
CFM meters can be installed in the air line to determine the amount of CFM available at a given location in a facility. Note that one BHP = 5-cfm.
Every AODD pump requires a certain amount of CFM to deliver the required LPM. Properly size the supply air hose and supply line to ensure an adequate amount of CFM is supplied to the pump.
Assume your air operated pump application requires 40-cfm at 80-psi to deliver 400 LPM. You installed 10- ft of 3/8-in air hose and wondered why it never achieved 400 LPM. The maximum CFM that can pass through a 3/8-in air hose is 30-cfm. The pump will never deliver the 400LPM because not enough CFM can be supplied to the pump to achieve the desired flow rate of 400 LPM.
If the supply air hose was increased to ½-in, which can pass 60-cfm, the desired 400 LPM can be achieved. The same scenario holds true for hard pipe. By increasing a pipe from 2-in to 2.5-in, CFM capabilities increase from 500-cfm to 2,000-cfm.
The size of the air hose and supply hard pipe is commonly overlooked and can create problems not only for air operated pumps but also for any pneumatic piece of equipment.
Remember the CFM and not pressure controls the speed of an air pump. Installing a needle valve after the regulator is the correct installation to achieve the desired speed of the air pump.
If an air pump must run at a constant speed regardless of supplied pressure, install a needle valve out of sight and set at desired CFM to maintain a constant speed for the air pump.
Global Pumps, a major provider for air operated diaphragm pumps, is an Australian based company founded in 1977 to fulfil the need for a versatile and service oriented specialist supplier, sourcing pumps and pumping systems from around the globe. Global Pumps deliver complete solutions for customers located throughout Australia and New Zealand, including a technical service division that performs onsite installations and servicing.
