Roots URAI-M Metric Blowers

The Roots Universal RAI (URAI) series is the standard when it comes to small rotary lobe positive displacement blowers.  They provide a pressure range of 1 to 15 psi or vacuum of 1″ to 16″ Hgg. Made of a cast iron casing and a pair of two-lobe impellers driven by steel timing gears and shafts, the URAI blowers have detachable mounting feet that allow them to be mounted in four different configurations.

The standard units, available in 17 different model sizes, use oil lubrication on the gear end and grease lubrication on the drive end.  The DSL (dual splash lubrication) models, available in 12 model sizes, feature oil lubrication on both the drive and gear end.

Available models:

URAI 22 24 32 33 36 42 45 47 53 56 59 65 68 615 76 711 718
URAI-DSL – – 32 33 36 42 45 47 53 56 59 65 68 615 – – –

URAI (US-Standard) vs URAI-M (Metric)

All of the model sizes listed above are available as US-Standard or metric units.  These units are identical except for two dimensions: the connection sizes and the shaft diameter.  On the US-standard units the connections are sized to NPT (threaded) and ASME (flanged), whereas the Metric unit connections are sized to BSP (threaded) or DIN PN10 (flanged).  On the US-Standard units the shaft diameter is sized in inches, whereas the Metric unit shafts are sized in milimeters.

US-Standard Shaft Size (Inches) Connection size
22 0.625 1.0 NPT
24 0.625 2.0 NPT
32 0.75 1.25 NPT
33 0.75 2.0 NPT
36 0.75 2.5 NPT
42 0.875 1.5 NPT
45 0.875 2.5 NPT
47 0.875 3.0 NPT
53 1.125 2.5 NPT
56 1.125 4.0 NPT
59 1.125 4.0 NPT
65 1.375 3.0 NPT
68 1.375 5.0 NPT
615 1.375 6.0 FLG
76 1.562 4.0 NPT
711 1.562 6.0 FLG
718 1.562 8.0 FLG
Metric Shaft Size (ISO 286-2) Connection size
22M 16 j6 1 BSP/ISO
24M 16 j6 2 BSP/ISO
32M 19 j6 1.25 BSP/ISO
33M 19 j6 2 BSP/ISO
36M 19 j6 2.5 BSP/ISO
42M 24 j6 1.5 BSP/ISO
45M 24 j6 2.5 BSP/ISO
47M 24 j6 3 BSP/ISO
53M 28 j6 2.5 BSP/ISO
56M 28 j6 4 BSP/ISO
59M 28 j6 4 BSP/ISO
65M 32 k6 3 BSP/ISO
68M 32 k6 5 BSP/ISO
615M 32 k6 150 PN 10
76M 38 k6 4 BSP/ISO
711M 38 k6 150 PN 10
718M 38 k6 200 PN 10

Is your unit a metric model?

Metric units in the URAI-M series will have an “M” in the model number and the part number stamped on the blower’s nameplate.  In the model number the “M” typically follows just after the number but could also be placed anywhere in the model designation.  In the part number you will see the “M” at the end followed by a letter indicating the drive shaft orientation. Here are several example nameplates:

45 M U-RAI metric Roots nameplate
56 U-RAI DSL HM metric Roots nameplate
47 M-DSL Roots metric nameplate

URAI-M Metric Parts and Replacement Units

When ordering replacement blowers you must specify if you need a metric unit as most Roots distributors will assume you are looking for a US-standard model if you do not specify.  Whenever possible, provide a photo of the nameplate on your current blower in order to get the correct replacement.  For repairs, overhaul kits contain all of the parts needed for a typical rebuild and these kits are universal for both the US-standard and Metric units.

Related Documents
NameTypeDownload
Roots URAI-M Metric Blowers spec sheet
Roots URAI Series
Roots Universal RAI, URAI-DSL, URAI-DVJ-DSL, URAI-G & Metric Series IOM
Roots URAI Series