FAQ: Air Operated Double Diaphragm Pump

Air-operated double diaphragm pumps, also known as diaphragm pumps, are used in a wide variety of industries. Here we address the most frequently asked questions about Air Operated Double Diaphragm Pumps.

What are the maximum operating temperatures for aluminum, PP and stainless steel diaphragm pumps?

  • Aluminium Pump:
    PTFE diaphragm : 120℃
    PE diaphragm : 60℃
  • Stainless Steel Pump:
    PTFE diaphragm : 120℃
    PE diaphragm : 60℃
  • PP (Polypropylene) Pump :
    PTFE diaphragm : 90℃

What is the Discharge Head of a diaphragm pump?

The Discharge Head is the vertical distance (in meters or feet) between the pump centerline and the point of free discharge or the surface of the liquid in the discharge tank.

What is the Suction Head of a diaphragm pump?

The Suction Head is the vertical distance (in meters or feet) from the centerline of the pump to the free level of the liquid to be pumped.

How to control the flow rate of a diaphragm pump?

Both air pressure and air volume affect the flow rate of the diaphragm pump. An air valve on the air supply line can be used to increase or decrease the amount of air and thus the flow rate. Be careful not to exceed the maximum allowable air pressure.

PTFE vs. PE: What diaphragm is suitable for my application?

When dealing with highly abrasive fluids, the right diaphragm material is critical to keep wear to a minimum. While PTFE is a good chemical resistant all-rounder, PE (polyethylene) is more resistant to abrasive fluids.

How to choose the right diaphragm pump?

The most important factors in selecting a diaphragm pump are

Main requirement: The fluid being pumped and the “wetted” parts (=parts of the pump that come in contact with the fluid) must be chemically compatible. Common wetted body materials are aluminum (inexpensive), polypropylene (good for acids and caustics), and stainless steel. There are several “Chemical Resistance Guides” available online (e.g. Pumpac Chemical Resistance Guide). In addition, if the fluid is above or below ambient temperature, the pump’s stated maximum operating temperature must be considered.

The flow rate must be appropriate for the application and determines the pump size. Typically, pumps are named for the diameter of the fluid inlet and outlet (e.g., 2″ diaphragm pump). Most pumps have the same size fluid inlet and outlet. As the pump size increases, the size of the fluid inlet also increases. For maximum efficiency, the pump should operate at approximately 50% to 60% of maximum flow. In general, slowing the speed will extend the life of the pump and also prevent abrasive wear.

Viscosity has a direct effect on flow rate, i.e. higher viscosities reduce flow rate. Note: Maximum flow rates listed are for non-viscous fluids such as water or solvents. The manufacturer should be able to provide the maximum allowable viscosity for the pump.

What are diaphragm pumps used for?

Fluid transfer is the most common application for air-operated diaphragm pumps. They are well suited for aggressive or abrasive fluids and are capable of pumping high viscosity fluids such as lotions, surfactants and resins. Diaphragm pumps are also capable of handling fluids with high levels of grit and solids and are often used for pumping slurries and heavily contaminated wastewater. Smaller diaphragm pumps are used for dosing, filling and dispensing applications. Diaphragm pumps can be found in virtually every industry, including paint, chemical, construction, water treatment, mining and others.

Typical Applications:

  • Transfer of liquids (e.g. tank to tank transfer or tank car filling)
  • Drainage and water removal (e.g. dewatering holds and waste water from holding tanks)
  • Spraying and cleaning (e.g. in filter presses and tank cleaning systems)

Typical Fluids:

  • Paints, pigments, resins, polymers, solvents and latex
  • Ceramic slips, frits and enamels
  • Glass and cutting slurries
  • Water