A silver metallic industrial double diaphragm pump with red caps and a central black manifold.

3D render of a silver metallic double diaphragm pump with red port caps and green seals

Stainless steel double diaphragm pump with black center body and red caps

Silver metallic industrial pump with a black rear housing and red caps on a white background

A stainless steel double diaphragm pump rendered against a white background

Metallic double diaphragm pump with red port caps on a white background

DP3X Series

2 Inch Stainless Steel Air Operated Double Diaphragm Pump

The DP31-50 is the two inch stainless steel pump in the DP3X series, and it is the model chosen when the fluid demands a material that aluminum cannot provide. 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 8.3 m dry. The 316 stainless steel center body and fluid caps resist corrosion from acids, alkalis, solvents and chlorides, and the pump weighs 56.9 kg, which is more than double the aluminum version but still manageable with two people. The stall free air motor ensures it starts under load every time, and the lube free system means no oil mist and no maintenance on the air line.

Maximum flow rate	172 GPM (651 LPM)
Maximum operating pressure	120psi (8.3 bar)
Suspended solids max diameter	1/4" (6.4mm)
Fluid inlet	Rp 2 (2" BSP, parallel) / 2" NPT
Fluid outlet	Rp 2 (2" BSP, parallel) / 2" NPT

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Key Benefits

What The Two Inch Stainless Steel Build Buys You

Corrosion resistance, durability and material compatibility come at the cost of weight and price, but they are necessary in some duties.

Built For Corrosive And Hygienic Fluids

316 stainless steel resists attack from acids, alkalis, chlorides and caustic solutions. It is the choice when the fluid will degrade aluminum or when hygiene standards require a non-porous, easy-to-clean surface.

Same Flow As The Aluminum Version

It delivers the same 651 LPM and 8.3 bar as the aluminum model, so there is no performance penalty for choosing stainless steel over aluminum.

Stall Free Operation Under Load

The pilot air valve gives a positive, fast shift signal to the major valve, so the pump does not stall at mid stroke and restarts immediately after a blockage.

No Oil Mist, No Maintenance

The self-lubricating air distribution system requires no oiler. There is no oil in the exhaust and no need to refill a lubricator during routine checks.

Lower Noise And Less Icing

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

Fits Where Your Old Pump Sits

Installation dimensions and footprint are compatible with the major AODD brands, so the base, pipe spools and air line usually stay unchanged during a swap.

Who It Is For

Who Buys This Pump

Two inch stainless steel is the choice when the fluid attacks aluminum or when the application demands a clean, non-reactive surface.

Chemical plants transferring acids, alkalis, electroplate liquids and quenching oils
Pharmaceutical and biotech facilities handling shear sensitive materials, additives and condiments
Food and beverage plants processing syrups, sauces and liquid ingredients where contamination must be avoided
Surface preparation shops using caustic cleaners, phosphates and degreasers
Water treatment plants handling chlorinated water, bleach and waste streams with high chloride content
OEMs building skid-mounted systems that need a durable, corrosion resistant pump

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.

An aluminum pump corrodes in acid or chloride environments, while this stainless steel version resists attack and lasts longer
A pump with a worn or degraded diaphragm fails in a sterile process, and stainless steel wetted parts reduce the risk of particle shedding
A centrifugal pump loses prime as the tank runs down, while this pump self primes and can be run dry without damage
A pump with a plastic air end fails under high pressure, while the stainless steel body and ceramic seals handle 8.3 bar reliably
A pump with a fixed elastomer fails in a changing fluid stream, and the model code allows you to change the diaphragm and ball for each duty

Application Scenarios

Where It Ends Up In A Plant

01

Chemical Transfer Between Tanks

The pump handles aggressive chemicals without corrosion, and the 8.3 m dry lift allows it to draw from a tank without a foot valve.

02

Pharmaceutical Formulation And Blending

The non-porous stainless steel surface and the ability to use PTFE or Santoprene diaphragms support clean transfer and reduce contamination risk.

03

Waste Water Treatment And Filtration

It feeds filter presses and dosing tanks with fluids that contain chlorides and suspended solids, and it can be dead headed without damage.

04

Tanker And Drum Unloading

Self priming with 8.3 m of dry suction lift, so it empties a road tanker or drum bank from ground level without a foot valve.

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)
Suspended solids max diameter	1/4" (6.4mm)
Fluid inlet	Rp 2 (2" BSP, parallel) / 2" NPT
Fluid outlet	Rp 2 (2" BSP, parallel) / 2" NPT
Air inlet	3/4" BSPT female (3/4" NPT available on request)
Maximum dry suction lift	27.2 feet (8.3m)
Sound level	70psi, 60 cycles/min., 80.5db(A)
Weight	125.4 lbs (56.9kg)
Pump Size	50-2"
Service Repair Kits	DP31-Air50 (air section); DP31-Flu50 - XX (fluid section), XX = Diaphragm Material, Ball Material
Model series code	DP31-50, DP31-Air50, DP31-Flu50-XX

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	316 stainless steel
Diaphragm options	Neoprene, Nitrile, Viton, PTFE/Santoprene, E.P.R, Acetal, Hytrel, Santoprene
Ball check options	Neoprene, Nitrile, Viton, PTFE, E.P.R, Acetal, Polyurethane, Stainless Steel, Hytrel, Santoprene
Seat options	Aluminum, 316 Stainless Steel, PVDF (Kynar), Carbon Steel, Santoprene, Hard Stainless Steel, Hytrel, Nitrile
Housing options	Aluminum (A), Cast Iron (C), Stainless Steel (S)
Center Body Mat	A-Aluminum / C-Cast Iron
Fluid Caps Manifold Mat	A-Aluminum / S-Stainless Steel / C-Cast Iron
Fluid Connections	N-NPT Threads / B-BSP Threads
Hardware	S-Stainless Steel / C-Carbon Steel

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 56.9 kg against 29.6 kg and a higher price. Choose aluminum when the fluid does not attack it and when weight and portability matter.
Versus the 2 inch cast iron version	Cast iron at 56.4 kg is the choice for abrasive slurry duty where wall wear matters. Stainless steel is the choice when corrosion or hygiene rules out iron.
Versus the 2 inch non metallic version	The polypropylene pump handles acids and alkalis that would eat aluminum, 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 8.3 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 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 Stainless Steel 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, which is 2 inch parallel BSP, or 2 inch NPT. The air inlet is 3/4 inch BSPT female, with 3/4 inch NPT available on request.