line with expansion joint: force on flange and on pump inner surface

i have a straight line with an expansion joint (without tie-rods) connected to a pump flange.

- line pressure is P
- expansion joint "inner hole" surface is S.

Let assume caesar gives force on pump flange node equal to 1000N.

Question: do the "1000N" contain both force on pump flange both the force on inner pump wall or not?

i mean: force on inner pump wall is P*S

is force on pump flange 1000N or 1000-P*S?