Key features
Material drops into an open throat under gravity and an auger on the coupling rod carries it to the pumping element, so the pump does not rely on the medium flowing to it.
Kinematic viscosity to 125,000 cSt and solids to 12%, well beyond what Roto rates its standard-suction ranges for.
W54 at 7 m³/h through to W73 at 150 m³/h, in close-coupled or bare shaft configuration.
W60 carries 48 bar at 28 m³/h. Above and below it the rating falls away, to 36 bar on the smallest sizes and 12 bar on the largest four.
Roto publishes identical capacity and pressure figures for both, so the bucket is chosen for how the material arrives, not for performance.
The stuffing box is externally mounted, so gland packing or a mechanical seal is maintained without dismantling the bearing housing.
About the Roto WM series
The inlet is the whole point of the WM. A conventional pump assumes the medium will find its own way into the suction. Plenty of media will not: dewatered cake, thick sludge, pastes, anything that sits in a heap rather than running. The WM answers that with a wide throat you drop the material into, and an auger on the coupling rod that takes it from the throat to the pumping element. Everything downstream of that is a progressive cavity pump; the throat is what you are buying.
The range runs 10 sizes, W54, W56, W58, W60, W62, W64, W66, W69, W72 and W73, from 7 to 150 m³/h, in close-coupled or bare shaft configuration. Roto rates it to 125,000 cSt, up to 12% solids and up to 150°C. The viscosity and the solids figure are the ones to hold on to. The standard-suction RD is rated to 30,000 cSt and the extra-large RL to 15,000, both at 7% solids. The WM is not a bigger version of either. It is the build you reach for when the medium is too heavy or too lumpy to feed a suction line at all.
Read the pressure column carefully, because it does not run the way size would suggest. The peak is in the middle of the range: W60 carries 48 bar at 28 m³/h. The three sizes below it sit at 36 bar, then it steps down through 24 and 18 bar, and the four largest sizes are rated to 12 bar. So a bigger WM is not a stronger WM. If you need both volume and pressure, that constraint decides the size before flow does.
Roto offers a standard bucket and an oversize bucket, and publishes the same capacity and pressure figures for both. Choose between them on how the material arrives and how much of it you need to hold at the inlet, not on duty. A custom hopper is available where neither suits the plant.
The honest limit is at both ends. If your medium runs into a suction line on its own, you do not need a wide throat, and a standard-suction pump will cost less to buy and take up less floor. At the other end, if the material bridges over the throat and stops feeding the auger at all, the WM cannot fix that either. That is what Roto's KM series is for, with a bridge breaker over the throat, rated to 3,000,000 cSt and 40% solids. Being honest about which of the three you need is the difference between a pump that runs and one that sits there turning in an empty throat.
Running dry is what kills these pumps. The stator is an elastomer wear part matched to the medium, and running dry destroys it: with no liquid carrying the heat away it burns out and takes the rotor with it, in minutes rather than hours. On a hopper-fed pump the throat emptying is a real and routine risk, so Roto's dry running protection device earns its place here more than on most duties. It screws a temperature sensor into the stator wall and trips the pump at a preset temperature.
Send us the medium, how it behaves at rest, the flow, the discharge pressure, the solids content and the temperature. We will tell you whether it is a WM, a standard-suction pump, or a bridge breaker, and we will say so even when the cheaper answer is the right one.
How the Roto WM works
The WM has two stages of handling, and only the second is the pump. First the material falls into the wide throat under gravity, where an auger mounted on the coupling rod turns with the drive and carries it forward to the pumping element. That auger does the job the medium would otherwise have to do for itself, which is why the WM will take pseudo-plastic material that would simply sit in a conventional suction.
The pumping element itself is a progressive cavity pair. A precision-machined single external helix rotor turns inside a double internal helix elastomer stator, and the rotor profile holds a sealing line along the axis of the pump, static and dynamic. Cavities form at the inlet end and progress along the pump to discharge, each revolution carrying a fixed volume. Flow is therefore metered and near enough non-pulsating, capacity is proportionate to speed, and the head the pump develops is not. Internal velocity is low, so shear-sensitive product comes through with minimum degradation, and the pump will handle a high percentage of solids in suspension without clogging.
Torque reaches the rotor through double-sealed cardan universal joints. Each joint uses two sets of perpendicular pins, which gives freedom of angular movement and smoother transmission of angular loads, and it is built to take the high axial forces that dominate in a progressive cavity pump. The stator has a tapered entry, which eases material in and improves suction capability. The bearing housing is separate from the wet end, so the medium is not contaminated by it.
The build is what you actually specify. Housings come in cast iron, cast stainless steel, fabricated steel or fabricated stainless steel, with rubber lining or epoxy coating where the medium attacks the casing. Rotors come in tool steel, case-hardened steel, alloy steel or stainless steel, with ceramic, tungsten carbide or hard chrome coatings for abrasive duty. Coupling rods and shafts are alloy steel or stainless steel, and Roto will quote duplex, super duplex, Alloy 20 and Haste Alloy where the chemistry demands it. Stator elastomers run natural rubber, nitrile, high nitrile, EPDM, chloro-sulphonated rubber, fluoroelastomer, Aflas and HNBR. That elastomer is the material decision that matters most: get it wrong for the medium or the temperature and the stator swells, hardens or is attacked, whatever the housing is made of.
Shaft sealing is gland packing or a mechanical seal. On the wide throat pumps Roto offers seal codes N, P, R, S and T, all rated to 25 bar. N and P are single-acting wave-spring seals, R and S single-acting multiple-spring seals. All four suit media carrying solids or running at high viscosity, on duties such as sewage, oil and water separation and food. T is a double-acting multiple-spring seal for abrasive, adhesive, crystallising, aggressive or toxic media, and for food, pharmaceutical and ceramic slurry work. Tell us the medium and the temperature and we will specify the seal with the pump, not after it.
Specifications
| Sizes | W54, W56, W58, W60, W62, W64, W66, W69, W72, W73 | wide throat |
|---|---|---|
| Flow rate | 7–150 m³/h | W54 to W73 |
| Pressure | 12–48 bar | W54 to W58 36 bar, W60 48 bar, W62 24 bar, W64 18 bar, W66 to W73 12 bar |
| Viscosity | up to 125,000 cSt | |
| Temperature | up to 150°C | |
| Solids handling | up to 12% | |
| Inlet | wide throat, auger on the coupling rod | standard or oversize bucket, both to the same published duty; custom hopper available |
| Configuration | close-coupled or bare shaft | |
| Housing materials | cast iron, cast stainless steel, fabricated steel, fabricated stainless steel | rubber lining or epoxy coating available |
| Rotor materials | tool steel, case-hardened steel, alloy steel, stainless steel | ceramic, tungsten carbide or hard chrome coatings available |
| Stator elastomers | natural, nitrile, high nitrile, EPDM, chloro-sulphonated rubber, fluoroelastomer, Aflas, HNBR | |
| Shaft sealing | gland packing or mechanical seal | Roto seal codes N, P, R, S and T to 25 bar |
Channel Pumps sizes and supplies the Roto WM. Send us the medium and how it behaves when it is left standing, the flow, the discharge pressure, the solids content and the temperature, and tell us how the material reaches the pump. We will come back with the size, the bucket, the stator elastomer and the sealing arrangement, and say plainly if a standard-suction pump would do the job for less.
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Frequently asked
When should you choose a wide throat pump over a standard suction pump?
When the medium will not flow into a suction line on its own. Dewatered cake, thick sludge and pastes sit in a heap rather than running, so they have to be dropped into an open throat and pushed along mechanically. If your medium does run to the pump unaided, a standard-suction pump costs less and takes up less floor.
What flow and pressure does the Roto WM cover?
The WM covers 7–150 m³/h across 10 sizes, at 12 to 48 bar. The pressure peak sits in the middle of the range rather than at the small end. W60 is rated to 48 bar at 28 m³/h, while the four largest sizes are rated to 12 bar.
What is the difference between the standard bucket and the oversize bucket?
The volume at the inlet, not the duty. Roto publishes the same capacity and pressure figures for both buckets on every WM size, so choose between them on how the material arrives and how much you need to hold at the throat. A custom hopper is available where neither fits the plant.
How thick a medium will the Roto WM handle?
Roto rates the WM to 125,000 cSt kinematic viscosity, up to 12% solids and up to 150°C. That is well beyond the standard-suction ranges, which Roto rates to 30,000 cSt and 7% solids. The stator elastomer still has to match the medium, so tell us what you are pumping and how hot it gets.
What is the difference between the Roto WM, RD and RL series?
The inlet, first of all. The RD and RL take a conventional suction connection; the WM takes a wide throat with an auger on the coupling rod. The RD covers 0.11–17 m³/h to 48 bar and the RL 14–420 m³/h at 6 bar, both rated to 7% solids. The WM covers 7–150 m³/h at 12 to 48 bar and is rated to 12% solids and a far heavier medium.
What sizes are in the Roto WM series?
There are 10. W54, W56, W58, W60, W62, W64, W66, W69, W72 and W73, available in close-coupled or bare shaft configuration.
What happens if the material bridges over the throat?
Then a plain wide throat will not feed, and the WM is the wrong build. Roto's KM series puts a bridge breaker over the throat for exactly that case, and is rated to 3,000,000 cSt and up to 40% solids. Tell us how the material behaves when it is left standing and we will tell you which of the two you need.
Can a Roto WM run dry?
No. Without liquid to carry the heat away the stator burns out and takes the rotor with it, in minutes. On a hopper-fed pump an emptying throat is a routine risk, so Roto's dry running protection device is worth fitting. It screws a temperature sensor into the stator wall and trips the pump at a preset temperature.