**Fundamental principles**

Isothermal change of state of gases** p_{0} x V_{0} = p_{1} x V_{1} = p_{2} **

**x V**applies when the change, the gas cushion in the accumulator, follows so very slowly when there is time enough for the heat exchange and, as a result of this, the temperature remains constant.

_{2}Adiabatic change of state of gases **p**_{0}** x ****V**_{0}^{k}**= p**_{0}** x ****V**_{1}^{k}**= p**_{2}** x ****V**** _{2}^{k }**occurs when the change of the gas cushions in the accumulator occurs quickly and the temperature remains constant. Under the operating conditions in practice, there are mostly polytrope changes of state being closer to the adiabates than to the isotherms. The oil volume available depends on the rated value of

the hydraulic accumulator and on the pressure ratio during the operation.

According to the technical conditions of the hydraulic system the adequate related value can be chosen by me ans of equations.

**Definitionen**

_{0}gas charging pressure

p

_{1}minimum operating pressure

p

**maximum operating pressure**

_{2}V

_{0}effective gas volume nominal volume at the same time

V

_{1}gas volume at p

_{1}V

_{2}gas volume at p

_{2}ΔV oil volume available ΔV = V

**– V**

_{2}

_{1}k adiabatic exponent (k = 1,4 for nitrogen uo to p

**=200 bar, over 200 bar k considerable difference)**

_{2}**Permissible pressure ratios**

*minimum pressure ratio*

The following applies to bladder and diaphragm accumulators: **p**_{1 }**≥ ****1,1 x p _{0} **

_{1 }should always be a little higher than the pre-set gas pressure p

_{0}in order to avoid constant impacts of the bladder on the oil discharge plug when the accumulator is empty.

*maximum*

*pressure ratio*The following applies to bladder accumulators: **p**_{2}** ≤ ****4 x p_{0}**

**V**

_{0}=0,16 – 2,0l,**p**

_{2}≤ 8 x p_{0 , }**V**

_{0}=2,8l ,**p**

_{2}≤ 4 x p_{0}**oil volume:**

_{0}, p

_{1}, p

_{2}, the gas volumes V

_{0}, V

_{1}, V

_{2 }change. The oil volume available ΔV iscalculated as follows: ΔV = V

**– V**

_{2}

_{1}