Front view of a black industrial double diaphragm pump with green trim and red port caps

Industrial air operated double diaphragm pump with black housing and red caps.

Industrial double diaphragm pump with black housing and red port caps on a white background

3D render of a black industrial double diaphragm pump with red ports on a white background

DP3X Series

1 Inch Cast Iron Air Operated Double Diaphragm Pump

The DP31-25 is the one inch cast iron pump in the DP3X series. It delivers 35 GPM, or 133 LPM, at up to 120 psi or 8.3 bar, with a dry suction lift of 6.1 m. The cast iron body resists wear from abrasive fluids and maintains structural integrity under high pressure. It runs on a 1/4 inch air line and is stall free, meaning it starts under load without hanging at mid stroke. The pump is designed for continuous transfer duty where the fluid is corrosive to aluminum or stainless steel, and where long-term mechanical durability matters.

Maximum flow rate	35 GPM (133 LPM)
Maximum operating pressure	120 psi (8.3 bar)
Suspended solids max diameter	1/8" (3.2 mm)
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 Cast Iron Build Buys You

Durability, pressure resistance and long life come at a higher weight than aluminum, but less than stainless steel.

The Most Durable One Inch In The Range

Cast iron resists wall wear from abrasive fluids like sand-laden water, slurry, or metalworking coolant with grit. It holds up better than aluminum or non-metallic materials under repeated high-pressure cycling.

Runs Dry And Dead Headed Without Damage

The pump can be run dry or blocked at the discharge without harm. This is essential for intermittent transfer, tank emptying, or systems with frequent valve closures.

Stall Free Air End With Faster Shifts

A pilot air valve gives the major air valve a positive, fast shift signal. This avoids mid-stroke stalls and reduces pulsation, which improves flow stability and reduces pipe vibration.

No Oiler On The Air Line

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

Quieter Than Most AODD Pumps

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

Fits Where Your Old Pump Sat

Installation dimensions and footprint match the major AODD brands. The base, pipe spools and air line usually stay the same when replacing another brand.

Who It Is For

Who Buys This Pump

One inch cast iron is the choice when the fluid is abrasive or the duty is continuous, and when the plant needs a pump that lasts through years of hard use.

Machine shops and metalworking plants transferring abrasive coolant, swarf-laden fluid, or quenching oil
Chemical and coating plants handling abrasive resins, pigments, or slurry-based formulations
Waste water and filtration plants moving grit-laden water, sludge or filter cake
OEMs building skid-mounted transfer units for harsh environments
Contractors who need one pump that handles abrasive fluids without frequent rebuilds
Plants replacing a competitor one inch AODD pump and unwilling to change the pipework

Problems It Solves

Problems This Pump Is Bought To Fix

Most enquiries for this model come from plants that have already tried other pumps that failed at one of these points.

A centrifugal pump loses prime when the tank runs low, while this pump self primes and runs dry without damage
A pump with a thin-walled body wears out quickly in abrasive service, while the cast iron wall resists erosion
A pump with a lube-fed air system leaks oil into the exhaust and requires regular topping up, while this one is lube free
A pump stalls at mid stroke under load, causing downtime and manual restarts, while this one shifts cleanly every time
A lighter aluminum pump cannot handle the mechanical stress of continuous high-pressure duty, while cast iron holds up

Application Scenarios

Where It Ends Up In A Plant

01

Coolant And Slurry Transfer

It moves abrasive metalworking coolant with chips and grit from sumps to holding tanks, and handles the same fluid in batch transfer without wearing out.

02

Tank Emptying And Sump Pumping

One person carries it to a pit or sump, drops in the hose, and runs it dry at the end without damaging the diaphragms or air end.

03

Chemical Transfer With Abrasive Additives

It transfers formulations with suspended solids like silica or pigments that would wear out a softer body over time.

04

Filter Press Feed And Recirculation

It can be dead headed as the filter cake builds and restarts cleanly when the cycle resets, without stalling.

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" (3.2 mm)
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" BSPT female (1/4" NPT available on request)
Maximum dry suction lift	20 feet (6.1 m)
Sound level	64.5 db(A) at 70 psi, 60 cycles/min
Weight	31 lbs (14.1 kg)
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, 1" DP31 METALLIC AODD PUMPS

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
Diaphragm options	1-Neoprene, 2-Nitrile, 3-Viton, 4-PTFE/Santoprene, 5-E.P.R, 6-Acetal, 9-Hytrel, B-Santoprene, G-Nitrile
Ball check options	1-Neoprene, 2-Nitrile, 3-Viton, 4-PTFE, 5-E.P.R, 6-Acetal, 8-Polyurethane, A-Stainless Steel, C-Hytrel, E-Santoprene
Seat options	1-Aluminum, 2-316 Stainless Steel, 3-Polypropylene, 4-PVDF (Kynar), 5-Carbon Steel, 8-Hard 400 Stainless Steel
Housing options	Center Body Mat.: A-Aluminum, C-Cast Iron, Fluid Caps Manifold Mat.: 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 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
1/4 inch NPT air inlet in place of the standard 1/4 inch BSPT, 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 14.1 kg against 8.6 kg. Choose aluminum when weight and portability matter more than wear resistance.
Versus the 1 inch stainless steel version	Same 133 LPM and same 8.3 bar, but 14.1 kg against 16.3 kg. Cast iron is lighter and cheaper, but stainless steel is better for hygienic or highly corrosive service.
Versus the 1 inch non-metallic version	The non-metallic pump handles acids and alkalis that would attack cast iron, at 177.9 LPM. Choose non-metallic for chemical compatibility, not for flow or durability.
Versus the 1-1/2 inch aluminum version	The 1-1/2 inch pump gives 340.7 LPM and passes 6.4 mm solids, but weighs 23.4 kg and needs a larger air line. Step up only when 133 LPM is not enough.
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.

Give It Real Air
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 2 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 Cast Iron 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 1-1/2 inch models at 6.4 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 BSPT female, with 1/4 inch NPT available on request.