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BOLENZ & SCHÄFER is a German company which invents the piston hydraulic accumulator in the year 1952. Until now it has been successfully asserting its leading positions in engineering, delivery and installation of equipment for power industry, metallurgy and a number of other industrial fields. In recent years the product range has been enriched with specialized railway hydraulics and pressure intensifiers. RHEA MP GMBH offers the following products:

  • Piston hydraulic accumulators
  • Piston hydraulic accumulator equipment
  • Pressure intensifiers
  • Pressure vessels
  • Railway hydraulics

BOLENZ & SCHÄFER was established in Dortmund in the year 1943. The plant for hydraulic accumulators and accumulator units in Eckelshausen – Germany has about 100 employees.

BOLENZ & SCHÄFER piston hydraulic accumulators

Piston accumulators
  • Piston accumulators with a volume of 1 up to 1500 litres and working pressure ranging from 220 up to 1200 bars.
  • Pressure vessels with a volume of 50 litres and working pressure of 220 and 360 bars.
  • Special accumulators for temperatures ranging from -40°С up to +80°С and working pressure of 375 bars.
  • Complete accumulator units, which are equipped with all the required accessories and safety devices.
  • Hydraulics for railway freight cars for bulk material – the hydraulic system with Bolenz & Schäfer piston accumulator is used for opening and closing the side flaps of freight cars.

The piston accumulators, the special accumulators and the accumulator units of Bolenz & Schäfer are delivered with all the documents and certificates required for their acceptance.

Application of the piston accumulators in hydraulic systems

  • As an energy collector in pulsation-type systems
  • For maintaining constant pressure
    • in cases of leakage
    • in cases of changes in the volume resulting from temperature differences
    • in cases of varied consumption in the hydraulic system
  • As an energy reserve in cases of critical necessity
  • For absorbing the pulsations
  • As a buffer / shock absorber
  • As an elastic element
  • As a regenerator of energy
  • Appropriate for being used with different fluids


The main components of Bolenz & Schäfer piston accumulators are:
  • A cast tube with a precisely machined internal surface, which is specially treated for achieving low friction and high reliability when the accumulator is operated under critical regimes
  • End caps, which are sealed on both sides with O-rings and are fixed by way of thread rings
  • A floating piston with a three-point sealing system. The volumes between the seals are pressure-free
  • A coupling with a return valve for gas filling in cases in which the accumulator is operated without a pressure tank (this coupling is not needed if a pressure tank is to be connected)

Mode of operation

One side of Bolenz & Schäfer piston accumulator is filled with nitrogen ( N2), class 4,0 up to the precharge pressure р0. The piston comes near the fluid-side end cap. When the pressure on the fluid side exceeds the precharge pressure by approximately 10%, the piston detaches itself from the end cap. The other side of the piston accumulator is filled with fluid under pressure and the gas is compressed until reaching the maximum working pressure р2. The quantity of the working fluid accumulated /stored/ under pressure can be supplied into the hydraulic system at any time for satisfying the need for high consumption at peak moments. The working pressure drops to р1.

Working process, setup and adjustment

Pressure control:
It is exercised by way of a manometer or a recording pressure gauge with a monitor. In certain cases they may as well perform switch-over functions.

Pressure adjustment:
The pressure is adjusted using pressure relays, contact-type manometers, change-over valves or adjustable pumps.

Position of the piston:
The position of the piston can be controlled by way of a shifting rod and/or a remote-control switch or an optical device which provides the opportunity for visualization. The newly developed КМЕ system allows continuous monitoring of the piston’s position.
The separate positions of the piston /degrees of loading/ can be programmed in a way which ensures that the functions are switched over. Data on the pressure values and the piston’s position can be transmitted to a central processor or controller and can be used for the purposes of the working process and the system’s setup.

Accumulator units

Bolenz & Schäfer piston hydraulic accumulators are extremely efficient when used together with an appropriate number of bottles of pressurized gas.
The use of the advantages of the flange connections for achieving high flow rate of the accumulator discharge at peak moments has various applications.

accumulator unit
  1. Bolenz & Schäfer accumulator unit with a horizontal accumulator for a hydraulic press

  2. Bolenz & Schäfer accumulator unit used in the alarm system of a ferryboat harbour

  3. Bolenz & Schäfer accumulator unit used as a compensator in submarine coastal prospecting for oil and gas

  4. Bolenz & Schäfer accumulator unit for casting equipment

Examples of application

Drilling rigs for oil and gas Drilling rigs for oil and gas

Bolenz & Schäfer piston accumulators are used as reserve supply in critical and emergency situations. They are offered with a complete set of the certificates required by the clients, such as: DNV, Lloyd's as per NS 5802, ASME or BS.

Electric circuit-breakers for high voltage Electric circuit-breakers for high voltage

Circuits switching over within milliseconds, which cut off the short circuit and prevent damages in cases of emergency. The piston accumulators of Bolenz & Schäfer provide powering for these switching devices under extreme temperature and weather conditions.

Urban transport buses and garbage trucks Urban transport buses and garbage trucks

Bolenz & Schäfer piston accumulators, light series are used for storing the energy created when the brakes are actuated, this making it possible for the vehicle to speed up to approximately 50 km/hr from a standstill without consuming any power from the motor and giving out only minimum emissions of exhaust gases.

Chill casting machines Chill casting machines

The accumulators are of particular importance to achieving the required casting speed of 8 up to 10 mtr/sec under a pressure of 210 bars. The piston accumulators of Bolenz & Schäfer are able to do it round the clock requiring only minimum maintenance. An example of it are the world’s largest chill casting machines, the power of which is 44 000 kN.

Hydraulic presses Hydraulic presses

It is within a short period of time that a high flow rate should be achieved under a pressure of 315 bars. The piston accumulators handle the abrupt rise in the pressure and compensate for the losses in the system. The picture shows a press with a flow rate Qmax=9000l/min for the manufacture of wooden particle boards. The press is equipped with 8 accumulators of Bolenz & Schäfer, each of them having oil capacity of 350 l, and 8 tanks under pressure, each of them having a volume of 1500 l of N2

Casting plants Casting plants

The high flow rates – up to 4000 l/min under a pressure of 120 bars – which are necessary for the repeated opening and closing of the punches as well as for the ejector control are provided by piston accumulator units.

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