Basic use of wearing rings in centrifugal pump

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Wearing rings

Wearing ring is a part of equipment (pump) which is used for reducing the internal circulation of liquid in the casing of a pump. Wearing rings are always used in pairs, one is installed inside casing, another one is impeller wear ring mounted on the impeller body (last). Sometimes stepped type or double wearing ring are used. This type of wear ring is used for special types of applications like hazards or high pressure. 

What is balance drum and disk in centrifugal pump

Wearing-ring
Wearing

What is the use of Wearing in centrifugal pumps?

Wearings are used for many purposes, these are the following.

  1. Reduce the internal circulation of the liquid inside the casing of the pump.
  2. Maintain a gap (clearance) between casing and impeller end to reduce the vibration level.
  3. Save from rubbing  each other,  and help pump impellers rotate freely in casings with very small clearances maintained in pump casings.
  4.  To prevent the liquid from entering from high pressure (discharge) into the low-pressure section side.
  5.  Improve pump performance approx. (3-5 %) and also increase the life of pumps and impellers.

Why wearing ring change in centrifugal pump?

To improve the performance of the centrifugal pump and reduce noise and vibration within the pump, when the clearance between both wear rings exceeds twice of  its original clearance value (as per equipment vendor recommendation) then the wearing needs to change.  This is the thumb rule for change. But before the change the wearing you have to go through your vendor recommendation or need to follow your company SMP (systematic maintenance procedure) in which you have already mentioned the clearance.

Wearing-ring-clearance
Wearing clearance
 

Types of wearing ring

In now days there are two types of wearing are use in modern centrifugal pumps.

  1. Single pairs
  2. Stepped or double paired

On the basis of installation inside the pump there are two types, these are described below

Stationary (Casing wearing) Casing wearing is stationary ring which is mounted within the inside of the pump casing.
Rotating (Impeller wearing) is a stationary part this types of wearing is  mounted on impeller.

in a centrifugal pump, there must be a running joint formed by a portion of impeller and a portion of casing separating the chambers forming the suction and discharging waterways.

What type of metrology use in wear ring?

Most of the material used for construction the wearing ring  depends on the nature of the liqued and its is as follows. Cast iron, Bronze, Manganese bronze.Nickel-aluminum bronze, Cast steel, 300-series stainless steel, 400-series stainless steel. For selection of the right wearing material there are many factors that need to be consider like as properties of  pumping liquid, temperature of fluid, nature of the fluid, pressure under the casing and flow rate of the liquid.  Sometimes used 410, 316, 316L SS (stainless steel), bronze, ceramics, cost iron etc.  it is totally dependent upon the inside fluid which have to transfer. The clearance between the casing and impeller wearing ring very sensitive because of the temperature difference bearing material expansion and squeeze. Therefore, it is the most important factor during the selection of appropriate bearing for the right pump.

waering-ring-materials
Wearing ring materials

How to replace wearing in centrifugal pump?

Now days many step has been taking to extract or replace the wearing ring from casing and impeller.  

  1. The first step is if loose all the the set screw between casing and wearing ring and very slowly hammer on inside near casing assembly, and try to to pull out if by this way not success.
  2. Take steel  rod the size of the rod should be almost equal to the diameter of inside wearing and weld the both end edge of the steel rod into inside the wearing and by the help of grinding machine,  cutting wheel try to little cut on opposite side of rod weld at two place after the little cut hit the road by hammers slowly slowly and you will see from cutting place wearing will be break and you can pull out easily and the same remove from the the impeller but in this case no need to who welding the rod.
  3. In some cases you can’t able to loose the set screw if it is not possible to lose then you can try another method with the help of drill machine and drill bit size should be equal to the outside diameter of the set screw and drill between casing and wearing at the place of the set screw and you will see screw has finished you can easily remove from impeller.
  4. And another method you can also try to pull it out by heating  it with oil or fire, or by  cooling it with  ice or liquid nitrogen.

How do you measure ring clearance between wearing rings?

To check clearance between casing and impeller wearing ring take, you can take help of filler gauge and measure at two place in opposite direction to each other measurement place. Alternatively, you can check the outside diameter of impeller wearing and inside diameter of casing wearing with the help of the inside micrometer and outside micrometer.

What is the use of wearing a centrifugal pump?

I have already discussed the use of wearing rings in centrifugal pumps, you can check from above details.

How wear ring is fitted to impeller?

The fitting of wearing on impeller depends on, what types of clearance has been considered by the vendor. It could be a transition fit,  in this scenario you have to heat the wearing and fixed it after that drill at the place of screw and tighten the screw. If the clearance between impeller and wearing the ring is shrink fit then you can easily slip on impeller drill and tighten the screw if the clearance is loose fit between them then you can take a help with tack tag weld in this scenario there is no need to tighten the screw but this type of situation is very little because nowadays every equipment vendor has given tight fit with his set screws.

How do you get a wearing ring off?

This is already mentioned and discussed in the above section you can check from here paragraph. you can check more details by following the links. wearing in other source 


General – up to 5 inches diameter 0.010 + 0.002 per inch diameter General – 5 to 10 inches diameter 0.015 + 0.001 per inch diameter For galling materials, add 0.005 inches  

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