In order to facilitate engineering calculation, there are usually two assumptions when calculating the average hydrostatic head height Hp:

(1) The work done by the liquid metal from the top level of the gate cup to the flow obstruction section can be expressed by the product of total mass m, gravity acceleration g and average calculated pressure head Hp, i.e. m g Hp;

(2) It is assumed that the cross-sectional area A of the casting (cavity) remains unchanged in the height direction.

Then the following equation can be written according to the diagram

In addition, the sum of the work done by W1 for filling the lower cavity and W2 for filling the upper cavity is the work done by these metal liquids (m) flowing through the blocking flow.

The formula can be substituted for:

The final simplification is:

In

Hp – average static head height (cm);

H0 – metal pressure head (cm) above choke section;

C – Total height of casting (cm);

Cavity height above P_choke (cm).