stuffing box pressure

[adula29]

How calculated pressure in the stuffing box, when the pump is overhung, single (e.g. OH1).
No back vanes, no balancing holes, closed impeler, Stuffing box is opened (Plan02 API)
Is there any simple solution?
Mechanical catrige single seal in stuffing box

 

[GPRnD]

The pressure distribution behind the impeller is a function of the vortex strength in that area. A number of books deal with the math in depth (I personally recommend "Centrifugal Pumps" by Johann Guelich).

Assuming no significant flushing flow, you can make assumptions that the vortex strength is about 0.5

The pressure at any point on the impeller is then:

p = p2 - 0.5 * rho * U2^2 * 0.25 * (1- r^2/r2^2)

Where:

p = pressure in N/m2
p2 = the pressure at the outlet of the pump impeller in N/m2
rho = the fluid density in kg/m3
U2 = the impeller rotational velocity at the OD of the impeller in m/s
r = the radius you want to determine the pressure at in m
r2 = the radius to the outlet of the impeller in m

 

[adula29]

But if I have closed impeller and balance holes it was true when I assuming that:
Suction pressure + 10‰ of Differential Pressure = Stuffing Box Pressure??
And is there any solution to calculate stuffing box pressure when impeller is cloded with back vanes.
In pump with closed impeller and back vanes, pressure distribution is reduced - but how much ...(of some kind engineering solution)
thx

 

[GPRnD]

For back vanes you use a modification of the formula I gave you.

In this case the vortex strength is no longer 0.5, but is a function of the vane height, vane diameter and axial clearance.

The formula for calculating the vortex strength is fairly complex and not easy to recreate with the simple text formatting they allow here.

I'd recommend buying or borrowing the book so that you get a full understanding of the issues. If you do, the formula I referred to is in table 9.3.


Your assumption for an impeller with balance holes is not unreasonable. However it depends on the sizing of the balance holes vs the wear ring clearances and whether you have a stuffing box bush as well as what external seal flush rate you are applying. For a more accurate estimate you need to calculate the pressure balance.

 

[adula29]

My assumption I based for information from "www" sides e.g.
this :

http://www.usseal.com/stuffingboxpressure.htm

I'm searching a simple, short, rough calculation for that examples.
Assuming: No external fluching


best regards Adam G.
Thanks so much for your help

 

[adula29]

Can I take this estimate for balancing holes and closed impeller?
Suction pressure + 10% of Differential Pressure = Stuffing Box Pressure??

 

[GPRnD]

Yes, your estimate is a reasonable one