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april 2011

The operation of shut-off valves

The shut-off valve allows correct dosage of fuel to the heat generator

What are the shut-off valves for?

The shut-off valves are fundamental components within modern thermo-hydraulic systems. In fact, these devices allow the flow of fuel to be regulated in such a way that the temperature of the fluid is not too high and there is no risk of damage to the system in response to pressure increases. Therefore, these valves are necessary to guarantee both the safety of persons in contact and in the vicinity, and to guarantee a longer life.
A fundamental aspect of these shut-off valves is that they allow positive safety or, once completely closed, they can only be reset by manual intervention by an operator. This is an essential aspect because the closure can also occur if the components of the valve itself break and the intervention can be useful to ensure optimal future operation.

How do the shut-off valves work?

The shut-off valves, for their application, can only be used in the fully open or completely closed position. In fact, there are no intermediate positions, which could lead to important problems such as cavitation and damage to the components of the system. In principle, the operation of the valves is based on a diathermic fluid which is connected to the shutter by means of a rod: when the temperature becomes too high, the rod pushes the shutter and leads to the closure of the tube.

There are various types of these valves, but the most common are the gate, ball or trottle valves.
- Gate valve: they are characterized by a wedge that moves perpendicularly with respect to the direction of the flow;
- Ball valve: it is perhaps the most common and is based on the rotation of a spherical shutter with a cylindrical cavity coaxial to the flow. When open, it basically constitutes a part of the pipe while if it closes it completely blocks the flow. This movement is very fast and this is both advantageous and disadvantageous: in fact, it can be the cause of water hammer for the system.
- Throttle: the shutter is a disk that rotates around an axis perpendicular to the direction of the fluid. In the event that the valve is in the fully open position, the pressure drops are minimal, while in partially open positions there are very high losses.
Gnali Bocia presents within its catalog valves made of forged brass: it guarantees fundamental characteristics for this type of component, namely strength and compactness, in addition to corrosion resistance.
As with all devices in contact with fluids, the installation, assembly and maintenance phases are fundamental for the duration and operation of the system. A good rule is to place the reset device in a vertical and not a horizontal position: in this way it is possible to safeguard the efficiency of the system without compromising it already in the initial stages.

Characteristics and subdivision of shut-off valves

The shut-off valves must, on the basis of what has been said, interrupting the flow when you reach excessively high values of temperature and pressure for the required application.
In particular, they must guarantee a substantially perfect seal when they are in the closed position and minimum pressure drops when they are in the fully open position. These aspects are fundamental because, if a perfect closure does not occur, the risk of system malfunctions would increase excessively and, if there were high pressure drops, there would be a reduction in the efficiency of the entire system. The intermediate positions present both problems in addition to the classic problem of cavitation, with all the consequences that follow from a functional, auditory and safety point of view.
There are numerous variants of the shut-off valves mainly based on the type of male that characterizes them. Another important subdivision is characterized by an abbreviation code consisting of two numbers. Some very popular and used examples are:
-    2/2;
-    3/2;
-    5/2;
-    5/3.
The first number indicates the number of ways that characterize and distinguish a particular type of valve (in this count the inlet and outlet are also considered), while the second number indicates the number of positions that the valve can assume during its operation. Referring to the subdivision above, for example, 5/2 indicates that there are 5 outlets and 2 characteristic valve positions.


See also
23/03/2020 Shelves for gas meters: available positions

23/10/2013 Shut-off valves prevent the risk of cavitation Cavitation is a harmful phenomenon that can affect valves operating in specific conditions, with the exception of shut-off valves

23/12/2020 The fuel shut-off valves: operation and advantages Everything you need to know about fuel shut-off valves: documents, composition and operation.

23/07/2020 Use the automatic air vents on heat sinks. An aid to the energy efficiency of the heating systems by using the automatic air vents.

23/05/2016 Shut-off valves and monitoring of fluid temperature The shut-off valve is a positive-action device that cuts the fuel supply

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