Double Diaphragm Pumps
State-of-the-art technology for reliable pumping applications

The Air-Operated Double Diaphragm pump or ‘AOD pump’ offers a wide variety of application possibilities and remains one of the most popular, reliable and versatile pumps on the market today. It is particularly notorious for its low initial cost, easy maintenance, simple installation and operation coupled with its ability to pump a wide range of fluids with varying viscosities, along with the seal-less, self-priming, dry running capabilities. Price Pumps offers one of the most advanced designs available today.

The concept and use of diaphragm pumps is one of the oldest pumping techniques used by mankind. In the early stages of development, the pumps were crude, mechanically driven, single membrane pumps with virtually no options available. Over the years, more innovative designs have continually progressed the pumps into their most common configuration of the modern world, namely the Air-Operated Double Diaphragm pump.

AOD pumps operate substantially different from conventional electrically driven centrifugal or positive displacement pumps. The general principle behind these pumps is to transfer fluid through the pump by means of a user supplied source of compressed air. The pump consists of suction and discharge manifolds, suction and discharge ball valves, liquid and air chambers. The air chambers are separated by diaphragms, which are in turn, connected by a common shaft. The final and most important component is the air distribution system. The compressed air is directed into the air valve. Through a series of passages, the air is directed into one of the air chambers. As one air chamber fills with air, the diaphragm in that chamber will begin to expand into the pump chamber, displacing the fluid in that pump chamber past the discharge valve into the discharge manifold. Conversely, the shaft that is connected to the opposing diaphragm pulls it into its own air chamber. This creates a vacuum in the pump chamber, which “pulls” the fluid past the suction valve and into the pump chamber. As the pump chamber reaches its maximum capacity, the diaphragm will trigger a switch, which reverses the air-flow to the opposite chamber and the process is repeated. The two pump chambers are always simultaneously in opposing cycles of the stroke: one is always discharging fluid while the other is in the suction cycle. This continuous redirecting of the compressed air causes the reciprocating motion of the diaphragms, which results in pumping of the process fluid.

Basic design
The basic design of AOD pumps, offers many advantages over other pumping alternatives. Because the driving force of the pumps is compressed air, the pumps do not require complex electrical and/or electronic controls to install and operate. The pumps handle a wide variety of fluids ranging from very high to low viscosity, to those that are corrosive and/or abrasive. They also have the ability to pump low-density powders and can pass fairly large solids. AOD pumps do not “shear” the fluid during transfer, so they are ideal for handling shear-sensitive media such as foods, paints and inks where fluid consistency needs to be maintained. Due to the diaphragms being fixed at the outer diameter bead, the pumps have static sealing surfaces and do not require mechanical seals. They are self-priming with lifts greater than 20 feet, and can run dry or against a closed discharge without damage. In some cases, they can even be run while completely submerged in the process fluid. For applications where performance needs to be varied, the pumps offer an infinitely variable flow rate without the need of a variable speed motor. Just by varying air inlet pressure the performance of the pump can be adjusted to suit the application. AOD pumps are portable and because of their quick and easy installation, they are easily transferable from site to site. Couple all of this with their ease of repair and maintenance, and you begin to see why these pumps have remained an industry favorite.

State of the art AOD pump
An excellent illustration of the most recent developments in the field of AOD pumps comes from the Price Pump Company (the company has a distributor in Belgium). First and foremost, this pump is the company’s patented oil-less, non-stalling air valve. The state of the art, “posi-shift” air valve design supplies a continuous high-pressure signal to the main spool, which insures reliable stall-free operation. This is ideal for all types of low-pressure applications where the pump can operate on inlet pressures as low as 5 psi. There is no need for springs or magnets that are present in other manufacturers designs. This means 100% customer confidence that the pump will start in the most difficult conditions of service, including troublesome frequent start/stop applications.

Non-wearing design
In addition to the stall-free design, the patented air valve consists of a main spool made from a highly engineered non-metallic material and precision-manufacturing techniques that allows for completely oil-less operation. It is because of this non-metallic spool material, that there are no metal-to-metal wearing surfaces, so there are no sleeves or O-rings required. The main spool is also hydraulically balanced, thus there are no additional side forces that cause excessive wear to the spool or housing. The result of the non-wearing design allows the user to operate the pump completely lubrication free, which results in several benefits. Aside from the obvious maintenance headaches and costs associated with oil pots, no lubrication means no oil misting into the environment creating an unhealthy working conditions. With no oil, lubricants or grease packed components being introduced to the system, there is no chance of contaminating the pumped product, if a diaphragm failure were to occur. The oil-less design has been field proven and working trouble-free since its introduction over 15 years ago. The end result is that the oil-less air valve design results in lower operating and maintenance costs and less downtime.

In addition to the oil-less, stall-free design, another main advantage is the fact that it accomplishes these benefits, while using the fewest air valve components of any major diaphragm pump manufacturer. The air valves require no O-rings, which is an advantage compared with some other brands. Anyone who has done maintenance knows what a hassle multiple O-rings can be during disassembly and re-assembly. Fewer parts means fewer problems. The externally serviceable main spool allows simple access into the housing, which makes inspection and/or repair quick and easy. There is never a need to disassemble the pump or take it out of service to inspect the main spool. Spool removal is very simple (see illustration).

Wide variety of materials
Depending on the different pumping performances required, the manufacturer offers a full line of AOD pumps, in sizes ranging from ¼” to 3”. A long list of fluids can be pumped due to the wide variety of pump and diaphragm materials available: pump bodies in metallic (Aluminum, 316SS, and Cast Iron) and non-metallic (Polypropylene and PVDF) designs; diaphragms, balls and seats in such materials as Neoprene, Buna, EPR, Viton, Teflon and the newly available material of Santoprene. The Santoprene diaphragms have a proprietary “full-faced”, long life design, and along with the other diaphragm designs, are not interchangeable with any other manufacturers parts. Any combination of pump body and elastomer materials can be used creating a number of possibilities available to meet the customer’s application and fluid requirements. In addition to the sizes and materials available, the main shaft of the pumps are nitrided, to provide longer life than standard non-treated 316SS shafts used by some other manufacturers. The pumps come standard with “whisper-quiet” polypropylene mufflers, with the option of a metallic muffler, when needed. The pumps feature NPT and ANSI flanges for the North American market with BSP and DIN flanges for the European market. There are clamped designs for general industry and bolted designs available for applications such as the petrochemical industry. If configuration is a key factor in the application, manifolds can be assembled in different directions to fit the required piping arrangement. For blending applications or if halving the pumpage is a requirement, a split manifold arrangement may be required, allowing a single pump to be used to pump two different fluids at the same time.