Do you repair Nash 904 series vacuum pumps?

Yes. Precise Mechanical rebuilds the Nash 904L/M, 904P/R, 904S/T and 904U, as well as the related 905 series, to original OEM tolerances. We are an independent shop in Houston and ship rebuilt and exchange 904 pumps nationwide.

What is the difference between a Nash 904 and a CL series pump?

The 904 is a two-stage liquid ring pump built to hold a deeper vacuum for services like condenser exhausting and process vacuum. The CL is a single-stage, high-volume pump used mainly for paper machine vacuum. Both are liquid ring pumps, but the 904 has two rotors in series and different internal parts.

Why won't my 904 pump reach its rated vacuum?

The usual causes are opened clearances in the first or second stage, internal leakage between stages from corrosion, air in-leakage past worn packing, or seal water that is too warm. A tear down identifies which. Resetting the clearances and repairing the castings restores the rated vacuum.

Do you have Nash 904 exchange pumps in stock?

We regularly stock rebuilt Nash 904 series exchange units. Inventory changes as pumps ship and cores return, so call 281-319-5595 to confirm the model you need is available.

Can you supply a new replacement for an old 904 pump?

Yes. Precise Mechanical manufactures new drop-in replacements for the 904L/M, 904P/R, 904S/T and 904U. They match the original mounting and connections, requiring minimal or no piping or baseplate modification.

Can a corroded 904 pump be saved?

Usually. We weld and remachine cast iron heads and bodies and can clad the water-contact surfaces in 304L or 316L stainless steel so the corrosion does not return. If the casting is beyond repair, we will say so and quote a new drop-in replacement.

Are you a Nash authorized repair center?

No. Precise Mechanical is an independent repair and manufacturing company and is not affiliated with or endorsed by Nash. That is what allows us to reverse engineer obsolete 904 parts and manufacture replacement pumps rather than being limited to OEM supply.

Nash 904 Series Vacuum Pump Repair

Repair & Service

Nash 904 Series Vacuum Pump Repair, Exchange and Replacement

Precise Mechanical repairs and rebuilds Nash® 904 series two-stage liquid ring vacuum pumps, stocks rebuilt 904 exchange units, and manufactures new drop-in replacements for the 904L/M, 904P/R, 904S/T and 904U. We are an independent liquid ring shop in Houston, Texas with over four decades of experience, and we also handle the closely related 905 series. Call 281-319-5595 for a rebuild, exchange or replacement quote.

What the 904 series is and where it runs

The Nash 904 is a two-stage liquid ring pump. The first stage handles the incoming air and vapor, discharges through an interstage passage into a smaller second stage, and the second stage discharges to atmosphere. Two stages in series let the pump hold a deeper vacuum than a single-stage pump of the same size, which is why the 904 shows up on services where the process needs to get well below what a couch pump ever sees.

Industry	Typical 904 series service
Power generation	Condenser exhausting and hogging, air removal from steam surface condensers
Refinery and petrochemical	Vacuum distillation, vapor recovery, process vacuum on reactors and strippers
Chemical	Filtration, degassing, solvent recovery
Pulp and paper	Deep-vacuum services such as suction press rolls, dryer and deaeration systems
Food, beverage and pharmaceutical	Vacuum drying, deodorizing, evaporation
General industrial	Vacuum impregnation, autoclaves, central vacuum

Because a 904 is often the pump that keeps a condenser or a distillation column at design vacuum, its failure affects the whole unit, not just one machine section. That is why we keep 904 exchange units on the shelf.

For the other Nash series we rebuild, exchange and replace, start at Nash vacuum pump repair.

904 models we service

Model	Rebuild	Exchange stock	New Precise drop-in replacement
904L / 904M	Yes	Yes	Yes
904P / 904R	Yes	Yes	Yes
904S / 904T	Yes	Yes	Yes
904U	Yes	Yes	Yes
905 series	Yes	Ask	Ask

Exchange stock changes as pumps go out and cores come back. Call to confirm the exact model and configuration you need.

What fails on a 904 pump

A two-stage pump has more internal surfaces to wear than a single-stage pump, and the second stage runs at a different pressure than the first. The failures we see most often:

Finding at tear down	Effect at the plant	Repair
First- or second-stage rotor-to-port-plate clearance opened by wear or scale	Loss of ultimate vacuum, longer pull-down, reduced capacity	Remachine or replace port plates, restore rotors, reset both stages to OEM tolerance
Scale and deposits on rotor blades, port plates and interstage passage	Falling capacity, rising amps, rotor imbalance	Clean, remachine, review seal water hardness and treatment
Cavitation erosion on second-stage surfaces	Noise, vibration, unstable vacuum at deep settings	Repair surfaces, correct seal water temperature or add a bleed
Shaft scoring at bearings and sleeves, bearing failure	Vibration, heat, seizure	Shaft repair or new shaft, new sleeves, bearings and seals
Corrosion of cast iron heads, bodies and interstage from acidic or chloride-bearing condensate	Wall thinning, internal leakage between stages, weeping	Cast iron welding, stainless steel cladding in 304L or 316L, remachining
Worn packing or mechanical seals	Seal water leaks, air in-leakage that limits vacuum	New sleeves, repack or reseal

Interstage leakage deserves a note. When corrosion or wear opens a path between the first and second stage, the pump may still turn and still pump air, but it will never reach its rated vacuum. It is a common reason a 904 gets tagged "worn out" when the real problem is a repairable casting.

How we rebuild a Nash 904 series pump

Every 904 goes through our seven-step repair process. On this pump the process includes:

Tear down and inspection. Both stages are disassembled, cleaned and measured. We record rotor-to-port-plate clearances, shaft runout, journal condition and casting wall thickness, and report the cause of failure.
Materials inspection. New and remanufactured parts are checked against current OEM specifications. Stainless lining is 304L or 316L.
Remanufacturing. Rotors, port plates, shafts, sleeves, heads and bodies are repaired or made new in our shop. Obsolete parts are reverse engineered from your pump.
Tolerances. Both stages are machined and set to original OEM tolerances.
Assembly. Every clearance is double-checked as the pump is built, with particular attention to the interstage fit.
Painting and coating. Primed and painted to your plant specification.
Final inspection. Free rotation, seal integrity and fit are verified before crating.

For 904 pumps that have run on aggressive condensate, we routinely clad the water-contact surfaces of the heads and bodies in 304L or 316L stainless. It stops the corrosion that caused the failure and extends the interval to the next rebuild.

904 exchange units

A 904 exchange puts a rebuilt pump on the truck to you now and takes your pump back as the core. For a condenser exhauster or a process vacuum pump that has failed during a run, it is the fastest recovery. Each exchange unit has been through the full seven-step process and set to OEM tolerances. See the exchange program (/repair-and-service/exchange-program).

How exchanges work, what is on the shelf and how cores are handled: vacuum pump exchange program.

New drop-in 904 replacement pumps

The 904 series has been in service for a long time, and OEM support for older configurations is not always available. Precise Mechanical manufactures new pumps for the 904L/M, 904P/R, 904S/T and 904U built to the original envelope, foot pattern and connection layout. They are drop-in, requiring minimal or no piping or baseplate modification, and can be built in cast iron or with stainless steel components for corrosive service. See Nash replacement pumps (/new-products/nash-replacements), and use our rebuild vs. replace vs. exchange guide to decide which route fits your situation.

Specifications for all Precise-built drop-ins are on the Nash replacement vacuum pumps page.

904 parts

We stock and machine 904 series rotors, port plates, shafts, sleeves, bearings, packing, seals and gaskets, and we reverse engineer parts the OEM no longer supplies. See vacuum pump parts.

More on repaired, clad and newly manufactured components: vacuum pump parts.

Sending a 904 pump to Houston

Rebuilds and exchanges ship nationwide from our Houston shop. Send the nameplate model and serial, the service, the symptom and photos, and we will return a scope and shipping plan. We confirm the turnaround with the scope after teardown. Our service area page covers freight and Gulf Coast logistics.

Frequently Asked Questions:

Do you repair Nash 904 series vacuum pumps?

Yes. Precise Mechanical rebuilds the Nash 904L/M, 904P/R, 904S/T and 904U, as well as the related 905 series, to original OEM tolerances. We are an independent shop in Houston and ship rebuilt and exchange 904 pumps nationwide.

What is the difference between a Nash 904 and a CL series pump?

The 904 is a two-stage liquid ring pump built to hold a deeper vacuum for services like condenser exhausting and process vacuum. The CL is a single-stage, high-volume pump used mainly for paper machine vacuum. Both are liquid ring pumps, but the 904 has two rotors in series and different internal parts.

Why won't my 904 pump reach its rated vacuum?

The usual causes are opened clearances in the first or second stage, internal leakage between stages from corrosion, air in-leakage past worn packing, or seal water that is too warm. A tear down identifies which. Resetting the clearances and repairing the castings restores the rated vacuum.

Do you have Nash 904 exchange pumps in stock?

We regularly stock rebuilt Nash 904 series exchange units. Inventory changes as pumps ship and cores return, so call 281-319-5595 to confirm the model you need is available.

Can you supply a new replacement for an old 904 pump?

Yes. Precise Mechanical manufactures new drop-in replacements for the 904L/M, 904P/R, 904S/T and 904U. They match the original mounting and connections, requiring minimal or no piping or baseplate modification.

Can a corroded 904 pump be saved?

Usually. We weld and remachine cast iron heads and bodies and can clad the water-contact surfaces in 304L or 316L stainless steel so the corrosion does not return. If the casting is beyond repair, we will say so and quote a new drop-in replacement.

Are you a Nash authorized repair center?

No. Precise Mechanical is an independent repair and manufacturing company and is not affiliated with or endorsed by Nash. That is what allows us to reverse engineer obsolete 904 parts and manufacture replacement pumps rather than being limited to OEM supply.

Talk to a Pump Expert

Get the answers you need from our experienced team. We’re here to help keep your operation running.

281-319-5595 Main Line

1-844-276-6274 1-844-276-NASH · Toll-Free

Down pump? Call Ken directly on the emergency line: 713-201-1589 or email Ken@precisemech.com.

Hours: Monday–Thursday, 7:00 AM–4:30 PM.

What to have ready: pump make, model, serial, and a photo of the nameplate.

Quick Links

Precise Mechanical

2414 Black Gold Ct,
Houston, TX 77073, USA

281-319-5595

1-844-276-6274 (NASH) Toll Free

Emergency Contact - Ken
713-201-1589
Ken@precisemech.com

Our Hours

Monday

7:00 - 4:30

Tuesday

7:00 - 4:30

Wednesday

7:00 - 4:30

Thursday

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