Step 1: usable volume
Add up the oil the cylinders draw from the reservoir at full extension (stroke × area, for each cylinder). The reservoir must hold all of it while keeping the suction strainer submerged even with cylinders out: as a practical reserve, add a generous margin over the calculated volume; on vehicles working on slopes, check the margin at the real inclination.
Step 2: cylinder differential
In double-acting cylinders the rod-side volume is smaller than the piston side: when the cylinder retracts, the difference returns to the reservoir and the level rises. The reservoir must absorb this variation without overflowing from the breather: it is the detail most often forgotten in multi-cylinder circuits.
Step 3: thermal check
The oil in the reservoir is also the circuit’s radiator. For the intermittent cycles typical of compact power packs, the volume from steps 1-2 is normally enough; for intensive or continuous cycles you must verify that generated heat (pump and valve losses) is dissipated; otherwise you need more litres or a heat exchanger. The calculator on our Tools page does the first check in 30 seconds.
| Step | What you calculate | Mistake to avoid |
|---|---|---|
| 1. Usable volume | stroke × area of each cylinder, plus a reserve margin | strainer uncovered with cylinders out |
| 2. Differential | volume difference between piston and rod side | oil overflowing from the breather |
| 3. Thermal check | heat to dissipate on intensive or continuous cycles | overheating oil: more litres or a heat exchanger needed |
Horizontal or vertical, plastic or steel reservoir?
Orientation is decided by the space available on the machine; material by environment and volume: plastic reservoirs cover the compact range with low weight and cost, steel takes over for larger volumes, high temperatures or aggressive environments. Gazzera makes both, from 1.5 to 30 litres, with dedicated plugs and suction kits.