Welch DuoSeal and CRVpro Rotary Vane Pumps

Rotary vane pumps are the workhorse of lab and industrial vacuum. They pump from atmosphere down to the 10^-3 and 10^-4 Torr range, back high vacuum pumps and run for decades with regular oil changes.

Welch has built rotary vane pumps for more than a century, and the DuoSeal belt-drive pump is one of the most widely installed lab pumps in the world. At Provac Sales, we supply Welch vane pumps new and rebuilt, and we repair and rebuild them in our own shop.

Welch Vane Pump Models We Carry

DuoSeal Belt-Drive Pumps

• Welch 1399 and 1400, small belt-drive pumps for instruments and small systems
• Welch 1376, about 300 L/min (10.6 CFM)
• Welch 1402, a mid-size belt-drive pump for freeze dryers and high vacuum lines
• Welch 1397 and 1374, high-flow belt-drive pumps for larger systems
• Welch 1405 and 1380, also offered as unmounted pump modules

ChemStar Pumps

• Welch 1376N, 1400N and 1402N, DuoSeal-based pumps prepared for chemical vapors

DirecTorr Direct-Drive Pumps

• Welch 8905, 8907, 8912, 8917, 8920 and 8925 direct-drive pumps
• Freeze dryer versions such as the 8917A-80 and 8960, 8965 and 8970 series
• Explosion-proof W models such as the 8917W and 8925W

CRVpro Direct-Drive Pumps

• Welch CRVpro 2, 4, 6, 8, 16 and 24 for lab and process use
• Welch CRVpro 30, 48 and 65 high-flow pumps
• Explosion-proof and chemical-duty CRVpro versions

Many listings are rebuilt units. Some show a price and others are quote-based. Each product page lists free air displacement, ultimate pressure, motor and oil capacity.

Belt-Drive DuoSeal vs Direct-Drive CRVpro

• DuoSeal pumps run slowly through a belt from a separate motor. The low speed keeps the oil cool and the vanes slow-wearing, which gives very long life and excellent ultimate vacuum. They are larger and louder than direct-drive pumps.
• DirecTorr and CRVpro pumps couple the motor directly to the pump. They are smaller, lighter and quieter for the same flow, and run at motor speed. CRVpro is the current Welch direct-drive line.
• ChemStar and chemical-duty versions add features for pumping solvent and corrosive vapors, and explosion-proof W and XP models suit hazardous areas.

How a Rotary Vane Pump Works

An off-center rotor turns inside a round housing. Vanes slide in slots in the rotor and are pushed against the housing wall.

As the rotor turns, the space between two vanes grows on the inlet side and draws in gas, then shrinks on the outlet side and compresses it until it opens the exhaust valve. Oil seals the gaps, cools the pump and lubricates the vanes.

Two-stage pumps put two stages in series to reach lower ultimate pressure. A gas ballast valve lets a small flow of air in during compression so water vapor does not condense in the oil.

Key Features

• Two-stage designs for deep rough vacuum
• Gas ballast on most models for pumping water vapor
• Long-life belt-drive DuoSeal design
• Compact, quiet direct-drive CRVpro pumps
• ChemStar, chemical-duty and explosion-proof versions
• Rebuildable with standard service kits

Applications for Welch Vane Pumps

• Freeze drying and lyophilization
• Backing diffusion and turbomolecular pumps
• Schlenk lines, manifolds and vacuum distillation
• Vacuum ovens and degassing
• Mass spectrometers and electron microscopes
• Refrigeration and HVAC evacuation

Welch Vacuum Pump Oil

• Use Welch DuoSeal oil, such as 1407K, in DuoSeal belt-drive pumps
• Use the oil Welch specifies for each direct-drive and CRVpro model
• Use a chemically resistant fluid, as specified by Welch, on chemical-duty pumps

See the product page or manual for the correct oil type and fill volume.

How to Choose the Right Welch Vane Pump

Before ordering, confirm:

• The ultimate pressure your process needs
• Free air displacement for your chamber volume and pumpdown time
• Whether water, solvent or corrosive vapors pass through the pump
• Belt-drive or direct-drive, and space and noise limits
• Supply voltage, phase and frequency
• Whether the area needs an explosion-proof motor

Maintenance Tips

• Change oil at the interval in the manual, and sooner when it turns dark or cloudy
• Run the gas ballast open for a while after pumping water vapor
• Check belt tension on DuoSeal pumps
• Fit an exhaust filter to catch oil mist
• Use a cold trap ahead of the pump on solvent processes
• Replace vanes, seals and gaskets with a service kit when ultimate pressure rises

Signs Your Vane Pump Needs Service

• The pump no longer reaches its rated ultimate pressure
• Oil mist or smoke at the exhaust
• Oil leaks at the shaft seal or gaskets
• Knocking, squealing or a slipping belt
• The motor runs hot or stalls on cold start

New vs Rebuilt Welch Vane Pumps

Welch vane pumps are built to be rebuilt. A rebuild usually includes stripping and cleaning the pump, replacing vanes, shaft seals, gaskets and exhaust valves, checking the rotor and stator for wear, and testing ultimate pressure after a fresh oil fill.

A rebuilt DuoSeal is a cost-effective way to keep a proven pump in service without changing the mounting, connections or motor wiring.

Welch Vane Pumps Repair

Provac Sales repairs and rebuilds Welch DuoSeal, ChemStar, DirecTorr and CRVpro rotary vane pumps. Submit an RMA request, complete the contamination data sheet and drain the oil before shipping. See our pump repair page for more information.

Related Welch Collections

• Welch scroll pumps, oil-free SCSpro pumps to replace oil pumps in clean labs
• Welch diaphragm pumps, chemistry-duty pumps for solvent work
• Welch dry pumps, WOB-L oil-free piston pumps
• All Welch vacuum pumps
• All vane pumps from every brand we carry

Find the Right Welch Rotary Vane Pump

Send us your pump model, required ultimate pressure, flow, process vapors and supply voltage. We will recommend the right Welch vane pump, confirm new or rebuilt availability, or quote a rebuild of your existing pump.

Browse our inventory above or contact our vacuum specialists at 831-462-8900.

Welch Rotary Vane Pump FAQ

1. What is the difference between a Welch DuoSeal and a CRVpro pump?

DuoSeal pumps are belt-driven and run slowly, which gives very long life and deep vacuum. CRVpro pumps are direct-drive, so they are smaller, lighter and quieter for the same flow.

2. What oil does a Welch DuoSeal pump use?

DuoSeal pumps use Welch DuoSeal vacuum pump oil. Use the oil specified in the manual and change it when it turns dark or cloudy.

3. What is a Welch ChemStar pump?

ChemStar pumps, such as the 1376N and 1402N, are DuoSeal-based pumps prepared for chemical vapors. Use them with a cold trap on solvent processes to protect the oil.

4. Which Welch pump should I use on a freeze dryer?

A two-stage pump with gas ballast is the usual choice. Welch offers freeze dryer versions in the DirecTorr line, and a 1402 DuoSeal or CRVpro 8 suits many lab freeze dryers. Send us your freeze dryer model and we will confirm the match.

5. How often should I change the oil in a Welch vane pump?

Follow the interval in the manual, and change oil sooner on dirty, wet or solvent processes. Dark, cloudy or foamy oil is a sign it is time.