Description
Welch Duo-Seal Belt-Drive Oil-Sealed Vacuum Pump 3/4 HP 115/208-230V 1725 RPM
The Welch Duo-Seal is a classic oil-sealed rotary vane vacuum pump with belt-drive design, widely used in laboratory, industrial, and HVAC applications. This unit pairs a Dayton 6K376D 3/4 HP motor with the proven Welch pump head on a steel base frame. It operates on single-phase AC power and is capable of achieving vacuum levels suitable for degassing, laboratory research, and general vacuum system requirements.
Specifications & What's Included
- Pump Brand / Model: Welch Duo-Seal
- Motor: Dayton 6K376D, 3/4 HP, 1725 RPM, H56 frame
- Voltage: 115V or 208-230V AC, 60 Hz, single phase
- Motor Current: 10.8A @ 115V; 5.3–5.4A @ 208-230V
- Drive System: Belt drive with 4L490 Demco belt
- Ultimate Vacuum Rating: Less than 0.05 micron at 300 RPM
- Tested Vacuum Performance: Approximately –28 in Hg (measured at our facility)
- Oil Type: Duo-Seal proprietary oil (required for operation)
- Mounting: Steel base frame with integral motor/pump assembly
- Manufacturer: W.M. Welch Manufacturing Co., Chicago, IL, USA
- Inlet / Outlet: Standard connections for laboratory vacuum systems
- Included: Pump, motor, base frame, and belt drive; oil NOT included (buyer must supply Duo-Seal oil)
Applications
Belt-drive oil-sealed rotary vacuum pumps are essential equipment in laboratory settings, industrial processes, and HVAC maintenance. Welch pumps are found in research labs performing degassing operations, vacuum filtration, and sample preparation. They are compatible with any system requiring 115V or 208-230V single-phase power and moderate vacuum levels. This vintage model dates from the mid-to-late 20th century, when Welch was a leading manufacturer of laboratory vacuum equipment. While older designs, these pumps remain in active use today in research environments, educational institutions, and equipment maintenance facilities, valued for their simplicity, durability, and reliable performance at moderate vacuum levels. The belt-drive design allows flexible speed adjustment and is quieter than direct-drive alternatives, making it well-suited to lab benches and continuous-duty applications.
This Welch Duo-Seal belt-drive vacuum pump has been powered and tested at our facility and is in good working order, pulling approximately –28 in Hg on our in-house gauge. The pump and Dayton 6K376D motor are mounted on a steel base frame. As a vintage industrial piece, it displays age-appropriate wear: paint loss and grime on the pump body, surface rust on the motor pulley and flywheel, and general patina throughout. The drive belt (4L490) is intact and in good condition. The unit ships via freight with the oil drained and removed — you will need to add the correct Duo-Seal proprietary oil before operating. Please view our photo set and contact us if you have any questions.
Warranty Information
Additional Information
Brand: |
Welch |
Model: |
Duo-Seal |
MPN: |
Duo-Seal |
Type: |
Belt-Drive Oil-Sealed Rotary Vacuum Pump |
SKU: |
46991 |
Motor Brand: |
Dayton |
Motor Model: |
6K376D |
Motor Power: |
3/4 HP |
Motor Voltage: |
115V / 208-230V AC |
Motor Current: |
10.8A (115V) / 5.3-5.4A (208-230V) |
Motor Speed: |
1725 RPM |
Motor Phase: |
Single Phase |
Motor Frequency: |
60 Hz |
Motor Frame: |
H56 |
Drive Type: |
Belt Drive |
Drive Belt: |
4L490 Demco |
Ultimate Vacuum: |
Less than 0.05 micron at 300 RPM |
Vacuum Achieved (Tested): |
Approx. -28 in Hg (measured at our facility) |
Oil Type: |
Duo-Seal proprietary oil (required) |
Pump Design: |
Oil-sealed rotary, vintage belt-drive |
Manufacturer Location: |
Chicago, IL, USA |
Country/Region of Manufacture: |
United States |
Power Requirements: |
115V or 208-230V AC, 60 Hz, Single Phase |
Form Factor: |
Benchtop / Base-Mounted |
Shipping Method: |
Freight – oil drained prior to shipment |
Seller Notes: |
Tested working at facility. Ships freight with oil drained. Buyer must add Duo-Seal oil before use. |
Review Status: |
Auto-Approved (needs review) 2026-07-04 |
Condition Notes: |
Welch Duo-Seal belt-drive vacuum pump tested and working at facility, pulling approximately –28 in Hg. Age-related wear, paint loss, surface rust on motor pulley and flywheel, intact belt. |
Motor Horsepower: |
3/4 HP |
Motor Current (115V): |
10.8 A |
Motor Current (208-230V): |
5.3–5.4 A |
Motor Frame Size: |
H56 |
Tested Vacuum Performance: |
Approximately –28 in Hg |
Manufacturer: |
W.M. Welch Mfg Co |
Country of Manufacture: |
United States |
Compatible Applications: |
Laboratory, industrial, HVAC degassing, lab research systems |
