Factors to be considered while selecting the AODD pump are as follows:
1.Fluid – The most important factor to be considered is the Type, Composition and Nature of the fluid in order to avoid the corrosion of the wetted parts and also to prevent the wear and tear of the pumping equipment. It is also necessary to determine whether the fluid is clean or contains some abrasive particles or slurries.
Nature of fluid:
a.) Corrosive fluid: Corrosive fluids like sulfuric acid, Nitric acid, Sodium hydroxide etc. destroys and damages the material when comes in contact with it. So a careful selection for the wetted part and diaphragm is needed.
For example for Sulfuric acid we can use PTFE/ Santoprene Diaphragm and PVDF as the wetted material.
b.) Abrasive Fluid: Abrasive fluids like Paints, Inks, ceramic slurry etc. which contains particulates that damages the contact material by scraping or wearing.
For example for Paints we can use PTFE Diaphragm and SS316 as the wetted material.
c.) Toxic Fluid: Toxic fluids like Lead, Mercury etc. has the quality of being toxic or poisonous. Diaphragm pumps don’t have seals hence they are suitable for such liquids. Further, containment duty type or leak detection for diaphragm is recommended for such liquids
d.) Flammable Fluid: Flammable fluids like Acetone, Benzene, Petroleum etc. that easily catches fire. Because AODD pumps are air driven, they are inherently explosion proof. However, some liquids may generate static charge, so pump should be completely grounded. We recommend to use ATEX certified pumps for such applications.
e.) Shear Sensitive Liquids: Liquids like tomato ketch-up, emulsions, paints, curd, when subject to shear (or churning), can change the product characteristics. Some liquids are shear thinning, some are shear thickening. Since AODD pumps run at lower speed, they are ideal for such liquids. We recommend to run the pump slower speed than normal for such applications.
f.) Vapor Pressure: Liquids such as diesel, hydrocarbons have low vapor pressure. We need to ensure that such pumps run at low speed and also the suction lift is limited, otherwise the pump may not deliver required flow.
2.Viscosity – Viscosity is resistance to the flow. In other words, we can say it the stickiness of the fluid. It is important to determine how viscous the liquid is. Depending on how viscous the liquid is, pump size needs to be determined. For example, it is better to use 1.5” size for liquids above 5000 cps.
Due to higher frictional losses in the pipeline for high viscosity liquid, the discharge pressure will be high. Customer to ensure proper suction and discharge pipe size.
Viscosity Correction Factor: For simplicity, AODD pump manufacturers provide viscosity correction factor for various viscosities depending on the pump size. The standard curves are generated with water- flow rate needs to be reduced by applying viscosity correction factor for high viscous fluids.
3.Pressure – Determining the pressure conditions at the suction(Inlet) and discharge(outlet) will help to select the appropriate pump size
a.Suction Pressure: Simply it is the pressure at the Inlet of the pump. AODD pump can work on both flooded suction as well as suction lift conditions as they are self priming. It is also important to determine if high suction pressure is there, since it may hamper the lifting of the suction valves affecting pump performance.
b.Discharge Pressure: It is the head requirement at the discharge of the pump. It is also known as delivery pressure i.e. at what height the fluid/Liquid have to be delivered along with frictional losses in the pipe line. If the discharge tank is closed then that pressure needs to be taken care as well.
4.Flow Rate – To select the size of the pump, flow rate is considered first. For higher flow rate one can select the larger pump with larger port sizes i.e. Suction & Discharge connection and vice versa. It can be measured in GPM or LPM or m3/hr.
5.Temperature – Pump materials have temperature limitations. We must know the operating temperature as well as ambient conditions to ensure the pump material is best suited for a particular application. For example, Neoprene diaphragm is limited to less than 100 Deg C
6.Service – AODD Pumps can be used for continuous as well as Intermittent application. It is mainly used for Unloading and Transfer Purpose. It is simple to operate & it can also be mounted on a movable trolley so that it can be easily used at the required place whenever needed with proper availability of compressed air.
7.Compressed Air Availability – As the name specifies i.e. AODD , it is Air Operated Double Diaphragm pump instead of Electrically/Motor operated. So first and the foremost thing it is necessary to ensure the availability of Compressed Air before buying the AODD Pump. It can also run on Nitrogen gas.
(Article is written by Vivek Shukla, Application Engineer at Madhav Fluid Solutions. He can be reached at vivek@madhavfluid.com or at +91 7045514302)