Activity: For your work ,you should be make the valve disassembly, inspection, test and reassembly.

Cartridge Valves is the interior of a control valve are off the shelf components with a standard, so that they are easy to fill a block owned by the valve. They are available in different configurations, on / off, proportional, pressure relief valves, etc. Life in general in a valve block and are electrically controlled to provide logic and automated functions.
Could you see simulate thus as below.

An altitude valve controls the level of a reservoir. The altitude valve will remain open while the tank is not full and will be closed when the reservoir reaches its maximum level. The opening and closing the valve requires no external power source (electric, pneumatic or power of man), it was done automatically, hence its name.
Control Valves
A control valve regulates the flow or fluid pressure. Control valves normally respond to signals generated by independent devices such as flow meters or temperature gauges. The control valves are normally fitted with actuators and positioners. Globe valves are widely used tire for control in many sectors, although quarter-turn types such as (amended), ball and butterfly valves are also used.
Regulation of the valves can also work with hydraulic actuators (also known as hydraulic pilots). These types of valves are also known as Automatic Control Valves. Hydraulic actuators in response to changes in pressure or flow, and open / close the valve. Valves automatiche di controllo non richiedono Sorgente di una alimentazione esterna, il che significa che la pressione del fluido è sufficiente per aprire e chiudere the valvola. Automatic control valves include: pressure reducers, valves, flow control, back support pressure valve, altitude valves and safety valves. An altitude valve controls the level of a reservoir. The altitude valve will remain open while the tank is not full and will be closed when the reservoir reaches its maximum level. The opening and closing the valve requires no external power source (electric, pneumatic or power of man), it was done automatically, hence its name.