Front view of a symmetrical industrial double diaphragm pump with a black manifold and a central gold filter.

A 3D render of a dark gray industrial diaphragm pump with red fittings on a white background.

Industrial double diaphragm pump with black housing and red port caps

3D render of an industrial double diaphragm pump with black housing and green accents

DP3X Series

2 Inch Cast Iron Air Operated Double Diaphragm Pump

The DP31-50 is the two inch cast iron pump in the DP3X series, and it is the model chosen when the fluid is abrasive or the duty is continuous and demanding. It moves up to 172 GPM, which is 651 LPM, at up to 120 psi or 8.3 bar, passes suspended solids to 6.4 mm and lifts 100 m dry. The cast iron center body and fluid caps make it robust for long term use in harsh conditions, and the stall free air motor means it starts under load every time instead of hanging at mid stroke.

Maximum flow rate	172 GPM (651 LPM)
Maximum operating pressure	120psi (8.3 bar)
Maximum air inlet pressure	120 p.s.i. (8.3 bar)
Suspended solids max diameter	1/4" (6.4mm)
Fluid inlet	Rp 2" & NPT 2"

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Key Benefits

What The Two Inch Cast Iron Build Buys You

Durability, wall thickness and material hardness sit differently on this model than on the aluminum or stainless version of the same hydraulic end.

The Heaviest Two Inch In The Range

It is the choice for duty where the pump runs for weeks without shutdown, and where the fluid carries grit, sand or metal fines that would erode thinner walls.

651 LPM With No Electric Motor

All the pump needs is a 3/4 inch air line. No motor, no starter, no VFD, no earthing and no electrical area classification paperwork.

It Will Not Stall At The End Of A Stroke

A pilot air valve gives the major air valve a positive, fast shift signal. The pump trips over cleanly instead of sitting at mid stroke waiting for someone to tap the air end.

No Oiler On The Air Line

The air distribution system is self lubricating and lube free, so there is no oil mist in the exhaust and nothing to top up on a maintenance round.

Anti Icing By Design

A built in vacuum chamber lowers discharge air pressure, which cuts both the temperature drop that causes icing and the exhaust noise. The published sound level is 80.5 dB(A) at 70 psi and 60 cycles per minute.

It Fits Where Your Old Pump Sits

Installation dimensions and footprint are compatible with the major AODD brands, so the base, the pipe spools and the air line usually stay exactly as they are.

Who It Is For

Who Buys This Pump

Two inch cast iron is the heavy duty choice. It goes in when the fluid is abrasive, the duty is continuous, and the plant needs a pump that lasts through years of service.

Foundries and metal processing plants moving sand laden coolant, slurry from shot blasting, and quenching oil with metal fines
Mining and quarrying operations transferring abrasive slurries, sludge and tailings from sumps to dewatering systems
Waste treatment plants handling grit, sludge and high solids content effluent
Manufacturing lines that run the pump 24/7 for bulk transfer, batching or system flush
Contractors who need one pump that handles both clean and dirty fluids without frequent replacement
Plants replacing a competitor two inch AODD pump and unwilling to change the pipework

Problems It Solves

Problems This Pump Is Bought To Fix

Almost every enquiry for this model starts with a pump that failed at one of these five things.

A centrifugal pump loses prime as soon as the tank runs down, while this pump self primes and can be run dry without damage
Line blockages deadhead the pump, and an AODD simply stops against the closed valve and starts again when the valve opens
Coolant and quenching oil carry chips and grit that wreck close clearance pumps, while ball checks pass solids to 6.4 mm
Electric pumps bring an area classification argument to a solvent store, and air drive avoids that argument entirely
A cast iron pump at 56.4 kg lasts longer than aluminum in abrasive duty, and the wall thickness resists erosion over time

Application Scenarios

Where It Ends Up In A Plant

01

Tanker And Drum Unloading

Self priming with 100 m of dry suction lift, so it empties a road tanker or a drum bank from ground level without a foot valve.

02

Batching And Blending Transfer

Air throttling gives smooth flow control from a trickle to 651 LPM without a variable speed drive, which suits recipe dosing into a mixer.

03

Filter Press And Filtration Feed

The pump can be dead headed as the cake builds and the pressure rises, then restart when the press is stripped.

04

Sump And Pit Emptying

One person carries it to the pit, drops the suction hose in and runs it dry at the end without burning anything out.

Technical Features

How The Air End Is Built

The hydraulic end of an AODD pump is simple. The air end is where pumps differ, and where Nuodean holds its patents.

Major Air Valve Plus Pilot Air Valve
The pilot valve is shifted mechanically by the actuator pin and pneumatically by the compressed air, then it shifts the major valve. That two stage signal is what makes the changeover positive and fast.
Dual Ceramic Dynamic Seals
Both the major air valve and the pilot air valve run ceramic dynamic seals. They resist wear, tolerate a dirty air supply and keep discharge contamination down over a long life.
Self Lubricating Lube Free Air System
No lubricator is fitted to the air inlet and none is needed, which removes both a maintenance task and the oil mist that a lubricated pump puts into the room.
Anti Icing Vacuum Chamber
The built in vacuum chamber reduces discharge air pressure, which lowers the expansion cooling that ices an air motor and drops the exhaust noise at the same time.
Interchangeable Installation Envelope
Port positions, foot spacing and overall envelope follow the major brands, so this pump can be dropped into an existing installation.
Selectable Wetted Materials
Center body, fluid caps and manifold, seat, ball check, diaphragm, connection thread and hardware are each chosen in the model code rather than fixed at the factory.

Specifications

Published Performance

Transcribed from the Nuodean data sheet published for this pump.

Maximum flow rate	172 GPM (651 LPM)
Maximum operating pressure	120psi (8.3 bar)
Maximum air inlet pressure	120 p.s.i. (8.3 bar)
Suspended solids max diameter	1/4" (6.4mm)
Fluid inlet	Rp 2" & NPT 2"
Fluid outlet	Rp 2" & NPT 2"
Air inlet	3/4" BSPT & 3/4" NPT
Model series code	DP31, DP31-50, DP3X

Materials

Material Options

Set in the model code. Ask us if you need a combination the code allows but the sheet does not show.

Wetted body material	Cast iron
Housing options	Metallic

Performance figures are transcribed from the Nuodean data sheet for this pump. Flow is measured at the pump discharge with water at ambient temperature; your duty point depends on air supply pressure, suction conditions, fluid viscosity and discharge head. Ask our engineers to confirm the duty point before you order.

Quality Control

Before It Is Crated

Every pump is run on air before it leaves, so the shift behaviour is checked rather than assumed
Sound level is published for the model at 70 psi and 60 cycles per minute so you can hold us to it
Ball, seat and diaphragm materials are checked against the ordered model code at assembly
The pump ships with the data sheet and both the fluid section and air section part lists

Customization

What You Can Change

Center body in aluminum or cast iron
Fluid caps and manifold in aluminum, 316 stainless steel or cast iron
Seat in aluminum, 316 stainless steel, PVDF, carbon steel, hard stainless steel, Santoprene, Hytrel or nitrile
Ball check in neoprene, nitrile, Viton, PTFE, EPDM, acetal, polyurethane, stainless steel, Hytrel or Santoprene
Diaphragm in neoprene, nitrile, Viton, PTFE with Santoprene backing, EPDM, acetal, Hytrel or Santoprene
NPT or BSP threaded fluid connections, stainless steel or carbon steel hardware
3/4 inch NPT air inlet in place of the standard 3/4 inch BSPT, on request

Comparison

Against The Alternatives

Where this pump wins and where you should be buying something else.

Versus the 2 inch aluminum version	Same 651 LPM and same 8.3 bar, but 56.4 kg against 29.6 kg and thicker walls. Choose aluminum when weight and portability matter, cast iron when abrasion resistance matters.
Versus the 2 inch stainless steel version	Same 651 LPM and same 8.3 bar, but 56.4 kg against 56.9 kg and lower price. Choose stainless when the fluid or the hygiene requirement rules out cast iron.
Versus the 2 inch non metallic version	The polypropylene pump handles acids and alkalis that would eat cast iron, at a lower 145 GPM. Pick non metallic on chemistry, not on flow.
Versus the 3 inch aluminum pump	The 3 inch reaches 237 GPM and passes 9.5 mm solids, but weighs 49.8 kg and needs more air. Step up only when 651 LPM is genuinely not enough.
Versus a centrifugal transfer pump	The centrifugal is cheaper to run at a fixed high flow with clean fluid. This pump wins when the tank runs dry, the line blocks, the fluid carries solids or the area cannot take a motor.
Versus the 2 inch triple diaphragm pump	The triple pump doubles fluid pressure to 14 bar for spraying and long lines. This pump gives more flow per unit of air when the pressure is ordinary.

Use Guide

Getting The Best Out Of It

Five things that decide whether this pump does 651 LPM or half of it.

Give It Real Air
Flow follows air. Use the full 3/4 inch inlet, keep the hose short and confirm the compressor can hold pressure at the flow the pump asks for.
Do Not Throttle The Suction
Throttle the discharge or the air, never the suction. Starving the suction is what causes cavitation, hard running and short diaphragm life.
Match The Elastomer To The Fluid
Diaphragm and ball material is chosen in the model code. Get the chemistry right and the pump lasts. Get it wrong and nothing else you do will save it.
Keep Suction Lift Honest
The published 100 m is a dry lift figure on the data sheet. Priming a flooded suction is always easier, so put the pump below the tank where the layout allows.
Stock The Two Repair Kits
One air section kit, DP31-Air50, and one fluid section kit, DP31-Flu50, coded for your diaphragm and ball material. Between them they cover almost every wear part.

Documents

Documents For This Pump

Straight from Nuodean's own literature: fluid and air section drawings, product data sheets, series catalogues.

PDF 2 INCH METALLIC AODD PUMPS DATA SHEET 1 Product Data Sheets PDF 1.2 MB Download PDF DP3X AODD PUMPS Catalogue Series Catalogues PDF 18.1 MB Download PDF Fluid Section of 2 inch DP11 Metallic Pump Fluid And Air Section Drawings PDF 151 KB Download PDF Air Section of 2 inch DP11 Metallic Pump Fluid And Air Section Drawings PDF 178 KB Download

Need a 2D or 3D CAD model of this pump? CAD on request via WhatsApp.

Answers

2 Inch Cast Iron Air Operated Double Diaphragm Pump FAQ

What flow will this pump actually give me?

172 GPM, which is 651 LPM, is the maximum with a free discharge and full air supply. Real duty points are lower. Send us the discharge head and the air pressure you can hold and we will tell you where on the curve you land.

Can it run dry?

Yes. An air operated double diaphragm pump can be run dry and can be dead headed against a closed valve without damage. That is the main reason plants choose one over a centrifugal pump.

What is the largest solid it will pass?

1/4 inch, which is 6.4 mm, on the suspended solids figure from the data sheet. If your fluid carries bigger solids, look at the 3 inch models at 9.5 mm or the heavy duty flap valve pump at 50 mm.

Will it replace another brand of two inch AODD pump?

Usually yes. The DP3X pumps are built so that installation dimensions and footprint are compatible with other brands. Send a photo of the nameplate and the pipework and we will confirm before you buy.

Which diaphragm should I order?

PTFE with a Santoprene backing for aggressive solvents and acids, Santoprene for general duty and long flex life, Viton for hot oils and aromatics, nitrile for petroleum products. Tell us the fluid and the temperature and we will put the right code on the quotation.

How loud is it?

80.5 dB(A) at 70 psi and 60 cycles per minute, as printed on the data sheet. Slower cycling is quieter, and a piped exhaust takes more off.

What connections does it come with?

Fluid inlet and outlet are Rp 2" and NPT 2". The air inlet is 3/4" BSPT female, with 3/4" NPT available on request.