The oil lubricated / gas operated piston of the DGS series is specially designed to have superior performance at higher gas pressures without the problems of other types of pistons: Gas lubricated / gas operated pistons cylinders have better sensitivity then oil lubricated pistons, however the natural drop rate at higher line pressure make them difficult to operate.
Oil lubricated pistons have no significant drop rate as the oil acts as a seal. There are a lot of deadweight tester manufacturers who claim oil lubrication / gas operation, but they use a traditional oil / oil piston and an oil-gas interface. The biggest and obvious disadvantage of this solution is that the surface level of the oil-gas interface precisely has to be known. The added uncertainty especially in high line pressure applications make this solution not ideal. The piston cylinder assembly of the DGS series is really different. The oil is lead to the gap between piston and cylinder by means of an oil reservoir around the cylinder. As the oil surface is slightly higher than the entrance bore in the cylinder the oil pressure is also slightly higher than the gas pressure ensuring enough lubrication between piston and cylinder.
The benefits of this design are:
- excellent turning time of the piston;
- very small fall rate (also at higher pressures);
- excellent leak rate, because the oil acts as a seal;
- the oil avoids dirt and dust entrance between piston and cylinder.
Mass / Weights Sets
The DGS gas deadweight tester series can be ordered with different mass sets. Generally it is delivered in kg. With the mentioned formula.
The table gives a list of masses corresponding with the ranges.
At the moment two different diameter of pistons are available but in the near future it will be expanded to more different pistons size: