Wear ring in centrifugal pump

[adula29]

Hello.
I have a question. Maybe is seems be a easy but I don't now what is the best solution in centrifugal pumps in wear ring.
Generally when we need use a serrated seal it is on the rotation part (on impeller). Once i saw a casing wear ring with serrate, and I have a doubt that it is a good solution.
Is it possible that serrate on stationary part of pump, (on stationary wear ring) can cause a pressure pulsation.
On the top of ring in gaps can appear a vapour or air?
THX for answer, and sorry for my english​

 

[1gibson]

These are called "Lomakin grooves." Typically on the impeller ring as you noted, but there should be no issues with having the grooves on the case ring. You do not want grooves on both surfaces.

 

[JJPellin]

You did not specify what type of pump. For a single stage pump, it probably doesn't make any difference. For a multi-stage pump, the rotor-dynamics will always be more stable if the grooves are on the stationary ring. And, the Lomakin effect would be maximized if there were no serrations. The addition of serrations can reduce the slip back through the wear ring clearances, but it will reduce the stiffness which could have a negative effect on rotor stability. The addition of a single groove in the stationary ring can improve the stability of a bushing. But, for a serrated ring, I would always place the serrations on the stationary ring.

Johnny Pellin

 

[GPRnD]

In the case of multistage pumps, serrating the stationary ring is a slightly better in terms of yielding better rotor stability (less cross coupled stiffness).

There are some papers that claim very shallow grooves will perform almost identically to smooth rings from a rotor stability standpoint, but give the benefits of reduced leakage rates.

I've never seen a wear ring cause pressure pulsations and I'm not sure how they could. Since the pressure drop across a wear ring is constant regardless of the geometry, what matters in vapor formation is the low pressure side fluid vapor pressure. Certainly in the case of a say a LNG service if your vapor pressure margin is too low you can get flashing, but that is a problem of correct pump selection for the conditions, not the wear ring design.