Venting the Stuffing Box 2

[Milkboy]

Hey Group

If you have a suction lift pump or a pump which has a vac during start up, you would expect to get some air trapped in the box. Am I correct with this?

Now if the pump was vertical, you could use a Plan 13 to keep the seal faces wetted and remove any trapped air.

If the pump with trapped air was horizontal, would the Plan 13 still remove all the air?

I ask as I have seen a video of a seal in a clear plastic pump which has air pumped in.
The air gets lodged at the seal and the message is that the air cannot be removed and will cause dry running.

If this is the case, how does the Plan 13 on a Vert application remove the air if the air gets trapped at the core?

TIA





-
Milkboy

 

[JJPellin]

In a horizontal pump, the air can be removed with either a plan 11 or 13. The plan 13 should be located at the high point and preferably sloped up to the conntection on the suction line or suction vessel. The plan 11 works because the centrifugal force with the pump running moves the air in toward the shaft and it can be forced under the throat bushing by the discharge flush. I have seen similar videos and even live demonstrations. They are usually done to sell pumps with special seal chamber configurations. Tapered bore seal chambers are supposed to be better at self venting.

When we overhaul a horizontal single stage pumps, we drill a small vent hole from the top of the seal chamber out to the inside of the head-side wear ring. Then, when the pump is flooded, it is automatically vented. On pumps where this is impractical, we add a vent valve so the operators can vent the seal chamber liquid full before starting up.

Johnny Pellin

 

[longeron]

The hole in the back plate that JJ describes is idiot proof.

A Plan 32 (injection of foriegn fluid into the seal chamber), a dual pressurized seal with a Plan 53, or even a dry gas seal with Plan 74 could also help if a dry start-up is a problem (overkill?). Some mfgs offer seal face combinations that will tolerate periods without lubrication too.

Another way get around the problem is with a Taper Bore seal chamber. Most of the ANSI OEMs offer seal chambers like this- a conical section opening up into the volute. Plain old Standard Bore or Big Bore seal chambers are usually have throat bushings or at least close off near the impeller. The Taper Bore box is also a good bet for processes with high concentrations of solids if you can't accept a Plan 32.