Air operated double diaphragm pumps for today’s marketplace The Air-Operated Diaphragm pump has evolved into the most commonly used in the world. Following a breif exmaination at its evolution and working, John Armitage looks at the features of the latest example from Price Pumps

used hv mankmci. In the earl\- stages of

dr\~elopment, I-he pimp\ ~veri’ crude,

mechanically driven, slnglc mcmhrane

,“““p with vlrtu,illy 110 oprioxs

:rvail;lhle. O\rr thr yv;lrs, more

inno\~anve designs ha\,e c~mtinually

prcgrecsed the pump Into their mart connncm ccmfiguration cd the modern

world, namely the Air-Operated

Double Diaphragm pump. L)ue ro

their low initial co\t, ea5y manten-

,mce, simple install;ltion and opera-

non coupled with their ahlliry to

puiup ;L wide r.~nge <>t tltlids with

varying vlscosltlt‘s. alon:: wlch the

seal-less, self-priinlnx:. drv running

capabiliries, It’s nc7 hurprise that the

Air-Operated Diaphragm (AOD@,)

pump has become, c~~~ct remams. one

of rhe rno\T pqx~lar, rellahle and

versatile pumps on the market today.

AOD@, pumps opcrarc ,uhsrantially

differently from ionvenrional electri-

cally driven centrifugal or positive

displacement pu11q7s

The genefill pnciple behmd AOD@,

pumps is to tranaier flud rhrough the

pump hy mean> <>I .I user+upplied

source of compressed air. The AOD’Q,

pump consists of juction and discharge

manifolds, suet ion ,+nrl discharge ball

val\~s. liquid ad au chamhcr5. The

air chamber5 are separated by dia-

phragms, which are in turn, connected

hy a common shaft.

Air distribution The final and rllilat 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

WORLD PUMPS nlay 2003

the au- chambers. As me air chamber

fills with air. the diaphragm in that

chamber will hegin to expand into the

pump chamber, displacmg the fluid in

that pump chamber past the discharge

valve into the discharge manifold.

Conversely, the shaft that is connec-

ted to the opposing diaphragm pulls it

into its own air chamber. This creates

a vacuumed In the pump chamber that

‘pulls’ the fluid past the auction valve

and info the pump chamber. As the

pump chamber reaches its maximum

capacity, the diaphragm will trigger a

switch that reverses the air-flow to the

opposite chamber and the process is

repeated. The two pump chamber:, are

always simultaneously in opposing

cycles of the stroke: one is always

discharging tluid while the other is in

the suction cycle. This continuous

redirecting of the compressed air

causes the reciprocating motion of the

diaphragms resultmg in pumping of

the process fluid.

The basic design of AODa pumps

offers many advantages over other

pumping alternatives. Hecause the

driving force of the pumps is com-

pressed 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 he maintained. Due to the

diaphragms being fixed at the outer

diameter bead, the pumps have static

sealing surfaces and do not require

mechanical seals. Tht,y are self-

priming with lifts greater than 20 feet,

and can run dry or agamst a closed

discharge without damage. In 5ome

cases, they can even he run while

completely submerged in the process

fluid. For applications where perfor-

mance 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 he

adjusted to suit the application. AOL>@

pumps are portable and because of

their quick and easy installation, they

are easily transferable from site to site.

Couple all of this with rheir ease of

repair and maintenance, and you begin

to see why AODD pumps have

remained an industry favorite.

innovation and

Having given a basic outline of the

general use, operation and advantages

of air-operated diaphragm pumps in

general, its time to look in detail at

the features in a Price AODa pumps

offer. First and foremost, is its paten-

ted oil-less, non-stalling air valve.

Cutaway diagram illusrates the basic

workings of a an AOD@ pump.

0262 1762/03 0 2003 ElsevIe Ltd All right,. reserved

The ‘posi-shift’ air valve design supp-

lie> ;I continuous high-pressure signal

to the main spool insuring reliable

stall-free operation. This is aimed at

types of low pressure applications

where the pump can operate on inlet

pressures as low as 5 psi. There is no

nerd for springs or lnagnets that are

present in other designs. These features

enable the pump to start in the most

difficult conditions of service, inclu-

ding troublesome frequent start/stop

applications.

Air valve Thr 011 less air valve design suns to lower qw-sting d maintenance cost\ ,md less downtime. The paten-

ted PriceB AOD” air valve consists of

,I nla~n spool made from a highly

engineered non-metallic material and

pr~ciaic,n-manuf~~cturiug techniques

rhat ;rllo~vs for oil-less operation. It is

hec:1115e of thiy non-metallic spool

m;lteri;ll, rh;lt rherc ;1ri‘ no metal- I( +tnct(ll wc,u-inp hurtace\, \o there

An AODV air valve

are no sleeves or O-rings required. The main spool is also hydraulically

halanced, so 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 pack-

ed components heing introduced

to the system, there is no chance

of contaminating the pumped pro-

duct, if a diaphragm failure were to

occur.

Along with the oil-less, stall-free

design of the Price@ AOD@ air valve,

another design feature 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 a huge

advantage compared with some

competitors air valves chat contain

many O-rings. Anyone who has done

maintenance knows what a hassle

multiple O-ringa can be during dis-

assembly and re-assembly. Fewer

parts means fewer problems. The

pump’s externally serviceable main

spool allows straight-forward access

into the housing, which eases inspec-

tion and/or repair. There is never

a need to disassemhle the pump or

take it out of service to inspect the

main spool.

Precision manufactured main spool

Price@ AOD@ pumps have a variety of

other features. Depending on differ-

ent pumping performances required,

Price@ offers AOD@ pumps, in sizes

ranging from I/” to 3”. A list of fluids

can he pumped due to the variety of

pump and diaphragm materials

available. Pump bodies are available in

metallic (Aluminum, 316SS, and Cast

Iron) and non-metallic (Polypropylene

and PVDF) designs. Diaphragms, halls

and seats are available in such

materials as Neoprene, Buna, EPR,

Viton@, Teflon@ and the newly avail-

able material of SantopreneD. Any

combination of pump body and elasto-

mer materials can he 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 Price @

AOD@ pumps are nitrided, to provide

longer life than standard non-treated

316SS shafts. The pumps come stan-

dard with ‘whisper-quiet’ polypro-

pylene mufflers, with the option of a

metallic muffler, when needed. The

AOD@ line features NPT and ANSI

flanges for the North American market

with BSP and DIN flanges for the

European market. Price has clamped

designs for general industry and bolted

designs available for applications such

as the petrochemical industry. w

CONTACT PriceB Pump Company 21775 Eighth St. East Sonoma, CA 95476, USA Tel: 800-345-7867 Fax: +I 707-938-0764 Email: sales@pricepump.com Website: http://www.pricepump.com

Price@ and AOD@ are registered trademarks of Price@ Pump Company. VitonB and Teflon@ are registered trademarks of DuPont Dow Elastomers. SantopreneB is a registered trademark of Monsanto Co.

m www.woridpumps.com WORLD PUMPS May 2003