# Pressure viscosity coefficient

> [HTML Version](pressure_viscosity_coefficient.html)

The pressure viscosity coefficient a is used for the calculation of lubricant film thickness. If the film thickness should not be calculated, you can just enter zero.

According to [ISO/TR 1281-2](bibliography.md#iso_tr_1281-2) the pressure viscosity coefficient a can be calculated by the kinematic viscosity n0 in cm2/s as $\alpha=0.1122\bullet\left(\frac{\nu_0}{10^4}\right)^0.163$

To calculate the reference viscosity n1, a value of $\alpha = 0.0077\bullet\nu^0.204$ using n in mm2/s and a in mm2/N is used according to [Baalmann](bibliography.md#baalmann_1994).

In the software, the proposal according to [AGMA 925](bibliography.md#agma_925) is used, because different oil types are considered. The pressure viscosity coefficient is calculated as $\alpha = k\bullet\eta_M^s$ , where ηM is the dynamic viscosity at operating temperature. The factors k and s are given for different lubricant types as shown in the following table:

| | | |
|------|------|------|
| **Oil type** | **k** | **s** |
| Mineral oil | 0.010471 | 0.1348 |
| PAO based synthetic non-VI improved oil | 0.010326 | 0.0507 |
| PAG based synthetic | 0.0047 | 0.1572 |




This formula is used if a lubricant from the list is selected. If ‘own input’ is selected, either the formula according to [ISO/TR 1281-2](bibliography.md#iso_tr_1281-2) 11.8 or according to [AGMA 925](bibliography.md#agma_925) or a direct input can be selected using the (./images/all_img3.png)-button next to the input field.