Vacuum jacketed vessels are particularly recommended for use with applications at low temperatures.
A vacuum jacket (outside the oil jacket) provides insulation, minimising cold/heat loss from the vessel and so improving efficiency. It means the outer surface of the vessel does not reach such extreme temperatures (reduced touch hazard), plus there is reduced frosting and condensation for improved contents visibility when cooling.
Vacuum jacketed vessel pistons feature double O-rings at the top of the piston, to further improve the sealing, particularly useful at very low temperatures. The design of these vessels ensures maximum isolation of the piston seal from hot/cold thermal fluid, by positioning the sealing O-rings in an environment surrounded by a vacuum, thereby minimising heat transfer.
Single jacketed vessels are a popular alternative. They are lower cost than vacuum jacketed vessels. They also take up less space (something to consider if using a Reactor-Ready Duo).