"The portable pump is a Liquid Ring Vacuum Pump (LRVP). It uses water as a sealing liquid. If the seal water is hot (because it's summer and the cooling tower is struggling), the pump capacity drops. Vapor pressure of the seal water increases, effectively reducing the pump's vacuum capability."
The volume-based calculation suggests a 20 L/s pump, but the outgassing-dominated calculation demands 101 L/s at the target pressure. Without the XLS, you would undersize by 5x. vacuum pump capacity calculation xls