Front view of a stainless steel pneumatic double diaphragm pump with green diaphragm rings and red port caps.

3D rendering of a stainless steel pneumatic double diaphragm pump with red port caps

Stainless steel industrial diaphragm pump with red port covers on a white background

Stainless steel double diaphragm pump with black center block and red port caps on a white background

Industrial stainless steel pneumatic double diaphragm pump with red port caps on a white background

DP3X Series

1 Inch Stainless Steel Air Operated Double Diaphragm Pump

The DP31-25 is the one inch stainless steel pump in the DP3X series, and it is the model chosen when the fluid is corrosive or the duty demands a durable, hygienic body. It delivers 35 GPM, which is 133 LPM, at up to 120 psi or 8.3 bar, passes suspended solids to 3.2 mm and lifts 6.1 m dry. The 316 stainless steel center body and fluid caps resist rust and chemical attack, and the pump weighs 16.3 kg, so it is light enough for one person to carry between stations. The stall free air motor ensures consistent start-up under load, and the self-lubricating system requires no oiler on the air line.

Maximum flow rate	35 GPM (133 LPM)
Maximum operating pressure	120 psi (8.3 bar)
Suspended solids max diameter	1/8" (3.2mm)
Fluid inlet	Rp 1 (1-11 BSP, parallel); 1-11 1/2 NPT
Fluid outlet	Rp 1 (1-11 BSP, parallel); 1-11 1/2 NPT

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Key Benefits

What The One Inch Stainless Steel Build Buys You

Corrosion resistance, durability and hygiene are the reasons to choose this over aluminum or cast iron in the same size.

Corrosion Resistant In Aggressive Fluids

The 316 stainless steel body withstands acids, alkalis, solvents and chlorides that attack aluminum and cast iron. It is the choice for chemical processing, pharmaceuticals and surface preparation where fluid integrity matters.

Lighter Than Cast Iron, Stronger Than Aluminum

At 16.3 kg it is 5.2 kg lighter than the cast iron version at 21.1 kg, but it does not suffer the same wall thinning under abrasion. That makes it better for long-term transfer of mildly abrasive fluids.

No Oil Mist On The Air Line

The air distribution system is self-lubricating and lube free, so there is no oil in the exhaust and no need to refill a lubricator during maintenance rounds.

Stall Free On Every Cycle

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

Quiet Operation With Low Noise

The built-in vacuum chamber reduces discharge air pressure, which lowers both the temperature drop that causes icing and the exhaust noise. The published sound level is 64.5 dB(A) at 70 psi and 60 cycles per minute.

Drop In Replacement For Other Brands

Installation dimensions and footprint are compatible with major AODD brands, so the base, pipe spools and air line usually stay the same when replacing a competitor pump.

Who It Is For

Who Buys This Pump

One inch stainless steel is the choice when the fluid is corrosive, the duty is continuous, or the plant requires a cleanable, durable body.

Chemical plants transferring acids, alkalis, and solvents between storage tanks and process lines
Pharmaceutical and biotech labs handling sterile or shear-sensitive liquids with minimal contamination risk
Surface preparation shops pumping quenching oil, electroplate liquid, and cleaning agents
Food and beverage facilities moving condiments, syrups, and additives where hygiene and corrosion resistance matter
Maintenance teams moving waste water, sludge, and tank cleaning fluids that attack aluminum
OEMs integrating a small, reliable pump into skid-mounted systems or cleaning rigs

Problems It Solves

Problems This Pump Is Bought To Fix

Most enquiries for this model come from plants that have already tried a different pump and faced one of these five issues.

An aluminum pump corroded in acid or chloride service, while the 316 stainless body resists those fluids without degradation
A cast iron pump wore through in abrasive slurry, while the stainless body holds up under moderate abrasion
A non-metallic pump failed under pressure or temperature, while the stainless version handles 8.3 bar without deformation
A centrifugal pump lost prime when the tank ran low, while this pump self primes and runs dry without damage
A competitor pump stalled at mid stroke and required tapping to restart, while the pilot valve design ensures clean, fast shift

Application Scenarios

Where It Ends Up In A Plant

01

Chemical Transfer And Formulation

The pump moves acids and alkalis between tanks and dosing units, with no risk of metal contamination or body corrosion.

02

Pharmaceutical And Biotech Processing

It transfers sterile liquids through clean-in-place systems, with a body material that meets hygiene standards and resists cleaning agents.

03

Tank Cleaning And Waste Water Transfer

It empties sumps and tanks of corrosive waste, runs dry without damage, and handles grit and sludge without clogging.

04

OEM Integration In Skid Systems

It fits into a compact skid for filtration, blending, or cleaning, where space, weight, and material compatibility are critical.

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	35 GPM (133 LPM)
Maximum operating pressure	120 psi (8.3 bar)
Suspended solids max diameter	1/8" (3.2mm)
Fluid inlet	Rp 1 (1-11 BSP, parallel); 1-11 1/2 NPT
Fluid outlet	Rp 1 (1-11 BSP, parallel); 1-11 1/2 NPT
Air inlet	1/4" BSP female (1/4" NPT available on request)
Maximum dry suction lift	20 feet (6.1m)
Sound level	64.5db(A) at 70psi, 60 cycles/min.
Weight	36 lbs (16.3kg)
Pump Size	25-1"
Service Repair Kits	DP31-Air25 (air section); DP31-Flu25-XX (fluid section) - XX = Diaphragm Material, Ball Material
Model series code	DP31, DP31-25XXXXXXX, DP31-Air25

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, G-Nitrile
Ball check options	Neoprene, Nitrile, Viton, PTFE, E.P.R, Acetal, Polyurethane, Stainless Steel, Hytrel, Santoprene
Seat options	Aluminum, 316 Stainless Steel, Polypropylene, PVDF (Kynar), Carbon Steel, Hard 400 Stainless Steel
Housing options	Center Body: A-Aluminum, C-Cast Iron; Fluid Caps Manifold: A-Aluminum, S-Stainless Steel, C-Cast Iron, METALLIC
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 316 stainless steel
Fluid caps and manifold in 316 stainless steel or aluminum
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
1/4 inch NPT air inlet in place of the standard 1/4 inch BSP, on request

Comparison

Against The Alternatives

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

Versus the 1 inch aluminum version	Same 133 LPM and same 8.3 bar, but 16.3 kg against 8.6 kg and full corrosion resistance. Choose aluminum only when the fluid is non-corrosive and weight is the main concern.
Versus the 1 inch cast iron version	Cast iron at 14.1 kg is lighter and cheaper, but it wears under abrasion and corrodes in wet or chemical service. Stainless steel wins for durability and longevity.
Versus the 1 inch non-metallic version	The non-metallic pump handles acids and alkalis that attack aluminum, at 177.9 LPM. Choose non-metallic only when flow and chemical resistance are both critical, and the duty is not abrasive.
Versus the 1-1/2 inch aluminum version	The 1-1/2 inch reaches 340.7 LPM and passes 6.4 mm solids, but weighs 23.4 kg. Step up only when 133 LPM is not enough and the fluid is non-corrosive.
Versus a centrifugal 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 1 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 133 LPM or half of it.

Use Full Air Supply
Flow follows air. Use the full 1/4 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 6.1 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-Air25, and one fluid section kit, DP31-Flu25-XX, 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: product data sheets, series catalogues.

PDF 1 inch DP31 metallic AODD pump datasheet 1 Product Data Sheets PDF 1.2 MB Download PDF DP3X AODD PUMPS Catalogue Series Catalogues PDF 18.1 MB Download

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

Answers

1 Inch Stainless Steel Air Operated Double Diaphragm Pump FAQ

What flow will this pump actually give me?

35 GPM, which is 133 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?

1/8 inch, which is 3.2 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 one 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?

64.5 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 1 (1-11 BSP, parallel) or 1-11 1/2 NPT. The air inlet is 1/4 inch BSP female, with 1/4 inch NPT available on request.