Design of a pressure balance with a small and calculable change of area with pressure

Abstract

The design and analysis of a pressure balance using a finite element method is described. The design precisely defines the pressure gradient in the gap and provides isolation from end-mounting effects. It also simplifies the finite element analysis. The change of area with pressure is calculated for four different operating modes, along with the gap profiles and pressure gradients. The sensitivity of the change in area with pressure to the piston-cylinder geometry, materials and fluid is analysed. The results indicate that the simple mode of operation (no external jacket pressure) is preferred as it produces a small uncertainty in the change of area with pressure and is easy to implement.

Pressure balance elastic distortion: experiment versus theory

“…The dominant uncertainty terms in this calculation are due to the spacing between the jacket seals j , Young's modulus (E = (601.6 ± 4) GPa) and the finite element deflections. The sensitivity coefficients differ from those found when calculating the elastic distortion coefficient [1]. In particular this measurement of A/A is insensitive to the value of Poisson's ratio whereas this is an important term when calculating the elastic distortion coefficient.…”

“…The model and design of the tungsten-carbide piston-cylinder unit has been described previously [1]. Figure 1 shows the piston-cylinder design and how the pressure is applied to the piston and cylinder.…”

“…Figure 1 shows the piston-cylinder design and how the pressure is applied to the piston and cylinder. The design is modified from that in [1]; there are now two jacket seals spaced j apart on the outer diameter of the cylinder and the pressure p j in this region can be varied independently from the operating pressure p s . The piston-cylinder unit can now be used in the controlled clearance mode; previously there was only one jacket seal so that p j was either equal to zero or p s .…”

“…The calculation method is described in [1]. Briefly, the finite element analysis is used to find the deflection caused by a ring of pressure applied to the cylinder and piston.…”

“…A recent approach to determine λ is to use finite element analysis to model the change in area of the piston-cylinder unit [1][2][3][4]. The finite element analysis method is used to determine the deflections of the piston and cylinder and can be used to find the pressure distributions in the gap between the piston and cylinder.…”