Volute (pump) - Wikipedia

Curved funnel that increases in area as it approaches the discharge port For other uses, see Volute (disambiguation).

A volute is a curved funnel that increases in area as it approaches the discharge port.[1] The volute of a centrifugal pump is the casing that receives the fluid being pumped by the impeller, maintaining the velocity of the fluid through to the diffuser. As liquid exits the impeller it has high kinetic energy and the volute directs this flow through to the discharge. As the fluid travels along the volute it is joined by more and more fluid exiting the impeller but, as the cross sectional area of the volute increases, the velocity is maintained if the pump is running close to the design point. If the pump has a low flow rate then the velocity will decrease across the volute leading to a pressure rise causing a cross thrust across the impeller that we see as vibration. If the pump flow is higher than design the velocity will increase across the volute and the pressure will decrease according to the first law of thermodynamics. This will cause a side thrust in the opposite direction to that caused by low flow but the result is the same – vibration with resultant short bearing and seal life.

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The volute does not convert kinetic energy into pressure – that is done at the diffuser by reducing liquid velocity while increasing pressure.[citation needed]

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The name "volute" is inspired by the resemblance of this kind of casing to the scroll-like part near the top of an ionic order column in classical architecture, called a volute.

Split volute

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In a split volute or double volute pump, the path along the volute is partitioned, providing two distinct discharge paths. The streams start out 180 degrees from each other, and merge by the time they reach the discharge port. This arrangement helps to balance the radial force on the bearings.[2]

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See also

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• Roots blower

generally double volute pumps are designed to reduced radial load on the impeller, this means smaller diameter shafts and bearings.
You may find that in a pump of this size, some of the manufacturers will have double volute design as standard as the pump has been designed for a higher duty ie, designed to operate at 960 rpm (50hz) or rpm (60hz).
For this duty there doesn't seem to be any advantage / disadvantage in either single or double volute. The main concern would be efficiency, reliabilty and capital costs.


Naresuan University
Phitsanulok
Thailand I would agree with Artisi especially on the efficiency. A small change in efficiency can add up to big dollars on large pumps that run often. I would also like to add that it could lower the cost for the supplier to manufacture the pumps substantially. With the double volute you have lower shaft deflection which normally means lower vibration. This is especially true if you are running with a VFD or throttling through a control valve. My thoughts would be to get what they quoted unless money is an issue and they offer large savings that would not be offset by higher operating cost because of lower efficiency.

Regards checman
What will be the system resistive curve and what will be the new pump performance curve.

You have the advantage of knowing the system perfectly well and this seems to me an opportunity to make sure that you get a pump that is perfectly suited to your system.

Yes, single volutes have more radial load on the shaft but the advantage is that the load is very predictable. We may not like radial loads but hey, bearing technology is very well devellopped.

A dual volute is basically two pumps in one casing. At one point or another depending on the design and on the machining quality and precision one of these pumps will shut off the other and radial loads will become unpredictable.

However, if your operation point is well known you will be able to stay out of troublesome operation area's regardless of the type of design.

Best regards.

Scalleke This is a great forum, the guys have many excellent comments.
I will add that the radial thrust problem is extremely important unless the pump operates continuously at or near the BEP .

A double volute scroll pump has almost no radial thrust at any point on the curve, from zero flow all the way out to well beyond the BEP. In other words, the double volute pump has little or no radial thrust reaction to operation above or below BEP.

But a single volute pump has a very pronounced radial thrust reaction when operated off BEP. If the bearings and shaft are insufficient to withstand the thrust, bearing and shaft life are shortened.

Many, perhaps even most manufacturers have stopped making the double volutes in the smaller sizes, Goulds being one of them. I and others have suffered trying to find double volute scroll pumps. I personally have given up and have gone to concentric, modified concentric, and turbine pumps instead. Your vendor may not be able to easily find a double volute in the size pump you need.

If that pump is forced to operate well off BEP for any length of time, I would strongly recommend you not accept a single volute pump.

Lastly, it is sad, but many manufacturers feel as though double volute is unnecessary in the smaller sizes, but they are wrong, even small pumps have serious problems with radial thrust.

PUMPDESIGNER I agree with all the above; one point to consider if you are forced to a single volute design ( it works for double volute also ) is that some pump manufacturers offer a larger diameter shaft and bearings for a relatively small extra cost. Another option is to check the shaft material and go for a better alloy, though this doesn't do much for the bearings. Again, the cost increase should be minor, and insignificant compared with the headache of a sudden broken shaft ! There seems to be some confusion as to double volute and double suction impeller pumps in this thread and one other currently active thread 407-.

The following has been posted there for comment.

My understanding is and I would welcome other comments:
1. A double suction pump is usually an axially split case unit with a single inlet dividing into 2 branches to a single double suction impeller, ie, flow to both sides of the impeller.
2. A double volute pump is one in which there are 2 outlets diametrically opposed to each other in a single casing which discharge into a single outlet branch.
3. A double suction pump can be either double volute or single volute design.
4. A single suction pump could be either double volute or single volute design.
5. A unit with more than 1 volute would be designated a multi stage pump.

Naresuan University
Phitsanulok
Thailand @ PUMPDESIGNER: as I was mistaking and referring my post to double suction pumps ; the explanation would be that uneven flow distribution can create axial disbalance which bearings are not designed for, leading to premature failure. (assumption is that in normal conditions double suction pumps have no axial load on the shaft)

as I can remember, this was an experience and an advice of my senior collegue which I heard a long time ago while we were discussing pump selection for a huge WTP; and this is the only reasonable explanation I can offer with my limited knowledge.