S PECIAL - FEATURE

Understanding and selecting air operated diaphragm pumps The simple concept behind the air oper- ated dkzpbragm pump has mad& it one of the major players in positive dis- placement pumping. Alfa Lava1 has provided many of these pumps to the process industries, and Its experience in their &sign and development makes it one of the great innovators in the field. Here the company offers an htro- duction to the subject and advises on bow you should consider selecting one.

The beauty of the air operated diaphragm (AOD) pump lies in its ability to pump a tremendous vari- ety of media. In the early days, it was marketed to the mining and construction industries, but it was soon applied to a wide range of products - from extremely shear sensitive media through to haz- ardous, aggressive and corrosive substances. Being of rugged, but compact construction, these

WORLD PUMPS NOVEMBER 1999

pumps have a low initial cost and an exceptional tolerance to variation in operating conditions. In the right application, the AOD pump is very diff- cult to fault.

g How does it work?

In short, the AOD pump uses air to drive two diaphragms within a pump chamber in a recipro- cating motion.This produces a suction effect to draw the product media into the pump and a dis- charge pressure to force the media out of the pump.

Figure 1 provides a more detailed illustration of the pump’s operation.This pump is a double acting positive displacement pump with two alternating pump chambers. Compressed air is supplied via the lubrication-free control valve to the rear of each diaphragm in turn. The com- pressed air acting on the back of the diaphragm forces it to move away from the centre block of the pump and force the pumped media out of the pump housing through the discharge manifold.

At the same time, the other diaphragm is mov- ing towards the centre block of the pump, causing a partial vacuum to be created in the second pump housing.This causes the pumped media to be pulled into the pump housing via the suction manifold.The two diaphragms are connected by a common piston rod, suction is therefore always occurring in one chamber while discharge takes place in the other.

The heart of the pump

At the heart of Alfa Laval’s AOD pump is an air valve system which provides a double action service, by distributing compressed air to each of the pump chambers. Precision manufacture ensures that the valve provides many cycles of operation and reliable service. All pumps are fitted with a lubrication-free system offering a much-reduced possibility of product contamination

It’s easy to assume that the diaphragms are just rubber discs that merrily move forward and backward within the pump.They are in fact the ‘work horses’ of air operated diaphragm pumps.

0262 1762/99/$ see front matter 0 1999 Elsevier Science Ltd. All rights reserved.

PECIAL FEATURE

Figure 1. Cutaway view of a double acting diaphragm pump.

~pksl adventages

Self priming Good dry running Suitable for installation in hazardous areas No mechanical seals Can handle abrasive media Easy installation and maintenance Variable flow by means of a regulator Can be operated against a closed valve

High displacement ratios are possible without the need for precision fits or the close tolerances between components found in other pumps. These ratios gener- ate the vacuum required to handle high-viscosity materi- als and trouble-free priming. The pumps’ excellent suc- tion can thus lift media from 6 m depth from dry, and 9 m once primed. Although the reciprocating action of the pump produces a some- times unwanted pulsating flow, its use on shear sensitive products is still appropriate. Solids up to 25 mm in diameter can also be easily handled without ill effect.

Compressed air can be easily controlled by variety of simple and inexpensive

devices.These will permit variable output vol- ume and pressure without the need for costly motor controls. The air drive also allows the pump to be operated in the most hazardous areas where electric drives would normally be prohibited. Gentle reciprocating action provides the media with a smooth flow path.

What about the bad points? Unlike rotary pumps (e.g. gear and progressing cavity types) the AOD pump is glandless - there are no mechanical or packing seals. With no rotat- ing parts and surfaces are statically sealed, creat- ing a leak free pump that can also run dry. Unlike some other pump types, the pump’s size and con- struction makes it ideal for installation into pro- cess lines where it may be used on a fured service or used around the process site on varying appli- cations. Normally, accidentally running positive displacement pumps against a closed valve will result in damage to the pumping element. Air operated diaphragm pumps are the exception to this rule. Should the pump be run against a closed or blocked discharge, it will simply stop.This is of particular benefit on filling machine applications.

Table 1. The pros and cons of air operated diaphragm pumping.

Air operation can be an advantage in explosive and hazardous areas but compressed air is a relatively costly utility in many plants. Compressors and air distribution systems are required, incurring high energy costsThe operat- ing concept also restricts application in areas where the product may contain fibrous material that would interfere with the operation of the pump. Where high flow and pressure rates are required, the AOD pump may not be capable of achieving them.

Concerns over the wear and tear of the dia- phragm may also restrict its application on

They have to cope with the demands of air pres- sure and of continuous flexing, whilst ensuring remaining compatible with the media, and resist- ing failure.

q A look at the good points

Typical dhmdwmtm Limited diaphragm life Relative cost of compressed air is high Pressures generally limited to 7 bar Not suitable for liquids containing fibrous material Pulsating flow

www.worldpumps.com WORLD PUMPS NOVEMBER 1999

S PECIAL - FEhWURE

NORTH AMERICA AUSTRALfA Ace Pump Amerloan Lewa Bsrnee Pumps Chempump Cole-Parmer Inetrument Crane Demlng Pumpa Cmnr Pumps b. Systeme Dorr-Cllver Edaon lntemrtlonal mowwrve

LLkzF”“” Qwer Manufaoturlng

Hypro CorpomtlotiSherwood Ingenoll~Dreseer Pumpr Ill A-C Pump Jaeco Pump Jeaoo America John Blue Company Kemlon Producb Komllne-Sanderwn Englneerlng Llnc Merketlng Maw, en Oemonloa Company Mliton Roy Compeny Muluqulp Nnptune Chemical Pump Company Dmmi;,a$ghwhg

Pulsafeeder, A unlt of ldex Cc Setfilco Snthw Dlvlrlon Shurfio Pump Manuhcturlng Technomeeter lnternationel Teledyne RepublldBpmgue ~M@W&-WMCo

lkebor lntemationrl Vema4ietlo Pump Wallace & Tleman Wanner Englneering Warren Rupp Wllden Pump & Einglnewlng Wlleon&ydar l%mgl Yamada America

v Kelalr Punlps Australia lrwrnw HalI i3 Son8 WrhpIKnpr !4c#la Pump Co Walker a Tlrnan plclflo Weir Englneerlng

Table 2. The three main material specifications and the applications they best suit.

r Awlkatlon are811 for air ouwated diamhranm Durnns Cast metal pump8 Far general indu.strller, water/ wastemd t3omWmorl~ Transfer duties Qeneral industrial applications Water treatment plants Waste treatment plants Construotion industry Mining industry ceranlios Filter prw feed

St&&s Aei’pumps For hygknic proceesea and d&ate media Food transfer Pharmaceutical applications Beverage duties Cosmetic applications ‘CiP’abie systems Age sensitive products Sterilisation systems Filter press feed

Non-metallic pumps For corrosion and abrasion resistance duties Chemical industry applications Corrosive media Aggressive media Environmental technology Hazardous applications Filter press feed

WORLD PUMPS NOVEMBER 1999 www.worldpumps.com

PECIAL FEATURE

m EUROPE Abel AGI Pompe Air Pumping Eng Services Alan Dale Pumps Alcon Pumps Alfa Lava1 Alltech Dosieranlagen Annovi Reverberi AR0 Corporation (UK) Asco Pompe ASTI 6.B.A Hranice Blagdon Pumps Bran + Luebbe Brimotor Burdosa UK Catag Charles S Madan 8 Co Chem Resist Group Cougar Industries Limited CT Pumps Datronix David Brown Union Pumps Group Deloule Espanola Denver Sala Division

Dia-Meter Pumps DKM, Dtvislon of Clextral Dominator Pump Dosapro Mltton Roy Energy Chemkal & Equipment EnviroTech Pumpsystems Feluwa Pumpen Flexachem Manufacturing Flotronic Pumps Flux-Ger&e Fluxinos llalla Fordwater Pumplng Supplies Ganz Energetics George Fischer Sales George Meller Grace Limited Grosvenor Pumps Hauke GesmbH 8 Co KG HR Holfeld (Hydraulics) Huedig lmovilli Pompe Ingersoll-Rand European Sales lwaki Europe Jabsco

JP Pumps Kinder-Janes Eng Linalex Limited Lutz (UK) Macro Precision Pumps Mencarelli Fompe e Valvole Michael Smith Engineers Milton Roy (UK) Munster Slmms Engineering Ntkkteo Deutschland NV AR0 SA

22 Pompe Cucchi ProMinent Pump & Package Reias Engineering Roach Pumps Roban Engineering Roper Induatrfes Europe S&Wood Setflfw Europe Seybert & Rahier

Shurflo Sigma Group Simaco Elettromeccanica SLH Construction Tapflo URACA Pumpenfabrik Verder Group Vergnet SA Victor Pumpen Wanner International Wirth Masch u Bohrg Fabrik Yamada Europe

ASIA

Asahi Industry Benxi Water Pump Factory Chemltreat Private Dynaflo lwaki

Koken Boring Machine Nikklso Sakura Seisokusho Yamada Yanmar Diesel Engine

INDIA - Candy Filters (India) Precidose Pumps

and Systems Swelore Englneering Vindl Accu-flow Vindi Vak Pump

Precidoae Pumps and Systems Swelore Engineering Vindi Aaxr-flow Vindl Vak Pump Water Supply Specialists

processes which could not operate economically three basic material specifications, together with should a break down in the process line take various special designs that ensure that there is a place. The reciprocating operation of the pump, pump available for most applicationsThe pumps which produces a ‘pulsing’ flow, can cause have high tolerance to difficult media, which pipework and process problems where a continu- means low viscosity, slurries, pastes, abrasive and ous product flow is required. Pulsation dampers shear sensitive media are common applications. are increasingly being installed to counteract Media with a viscosity range of 0.7 to 25 000 CPS this problem. can be transferred.

111 A pump for (almost) every task

AOD pumps provide the optimum solution to many fluid transfer problems. Alfa Lava1 supplies

More recently, the Alfa Lava1 AOD pump has been developed to provide a range of pumps for powder transfer applications. In addition to this, a range of high pressure cast metal pumps have been introduced for discharge pressures of up to 21 bar, where closed or restricted discharge is required or where the available air pressure is abnormally low.

www.worldpumps.com WORLD PUMPS NOVEMBER 1999

S PECIAL FEATURE

Table 3. Typical materials of construction and their limitations.

of eon and thnitationr Pump connection sizes (mm) Materials

Displacements Maximum pressures (bar)

Maximum temperature (“C) Cast metal pumps

Plastic pumps

0 Selecting an AOD pump

One of the primary considerations for selecting the air operated diaphragm pump is to ensure that its valve system is not only durable but reli- able.Air quality and maintenance in the facilit) should also be considered. Some additional selec- tion factors include.

l What is the flow rate and pressure required ? l Does the product have any suspended solids ? l Is a wet or dry suction lift required ?

l What is the media viscosity ? l Will the pump be required to run dry ? l Is it possible that the discharge line may be

closed or become blocked during normal operation ?

8, IO , 15, 25, 40, 50, 80 Aluminium, Polypropylene, PTFE, Ductile iron, Stainless Steel 0.05 to 45 m3/hr Cast metal 7 Plastic 5 High pressure 21

NRS Internals 80 EPDM/NBR Internals 90 FKM, PTFE 120 Polypropylene 60 PTFE 120

Air operated diaphragm pumps are built in a variety of materials to satisfy the product media to be pumped and the application where the pump is to be used. Pump sizes are chosen depending on the flow rate of product media required.

We have now reviewed the basics of the air operated diaphragm pump looking at its opera- tion, its good and bad points. specifications and the various areas of its application. The pump in essence is a ‘great little mover’, which can pro- vide a cost-effective solution to many pumping applications.

For more information, visit the Alfa Lava1 web- site on www.flow.alfalaval.com Alternatively, contact the Alfa Lava1 ‘positive displacement pumps’ customer support group based in Eastbourne, UK. Tel: +44 1323 412555.

WORLD PUMPS NOVEMBER 1999 \vww.worldpumps.com