Suction cups. What are they, types, where to place them and dimensioning.

Do you want to know the function of suction cups in your irrigation system, the types that exist and what are the consequences of not having them? In this post we explain it to you in detail.

The biggest problem that can appear in an installation without suction cups is the presence of air. The main causes for which this fact can occur in hydraulic pipes are:

• Filling and emptying operations.
• Temporary interruption in the water supply.
• The phenomenon of vortices in the suction of the pumps.
• The appearance of cracks in areas of negative depression.
• The release of dissolved air.

The consequences of the presence of air pockets or dissolved air in the water are:

• Overpressures: due to the easy compressibility of the air that is retained in the water.
• Reduction of the passage section of the pipe and the flow of water: it leads to an increase in the electrical consumption of the pumps and their loss of performance.

The reduction of the section also causes an increase in load losses and the possibility of cavitation, corrosion, noise, vibrations and structural deterioration inside the pipes, changes in the speed and friction of the water with the wall of the pipe. tube, errors in the instruments for reading or measuring water, etc.

For all this, the presence of suction cups in hydraulic systems is necessary.

What are suction cups?

The suction cups are protective elements that are placed in the hydraulic installations to prevent overpressures and depressions in the system. Its about aeration valves that introduce and/or extract air from the pipe to the outside, depending on the pressure difference between the pipe and the outside environment.

Generally, a suction cup is a cup-shaped body that has a hole with a lid on the top, while the bottom part has a flange or thread that connects to the pipe. Inside it is the shutter mechanism: a spherical or cylindrical-shaped float that obstructs the hole in the upper part to thus close the device. The sealing of the suction cup is ensured by a gasket made of rubber or another synthetic material.

 

Types of suction cups

Classification according to the size of the hole:

• • Large hole suction cups: Large hole suction cups are those that have a ø >25mm. They allow the entry or exit of air when the pipe is filled or emptied.

 

• • Small hole suction cups, automatic or purgers: These are devices of reduced dimensions to allow their opening when the system is pressurized. The air outlet hole is ø < 12mm. They are usually used to expel small amounts of air accumulated in the installation during operation normal of it.

Classification according to their function:

• Monofunctional or simple effect suction cups: Only perform one of the following functions:
  1. Air expulsion during the pipe filling operation.
  2. Admission of air during the emptying operation of the pipe.
  3. Air expulsion when the system is pressurized and the water circulating through it.

Within the monofunctional suction cups are included the purgers and unidirectional suction cups (the air circulates in a single direction inside them). Monofunctional suction cups are similar to those with a large hole, and in turn are divided into vacuum suction cups (they are used when a negative pressure must be present in the conduit, such as in the expulsion of air to prime a siphon at its highest point ), and adductors (used for the admission of air in large quantities without its possible exit).

• • Bifunctional or double effect suction cups: These suction cups are capable of expelling air during the filling operation and admitting air during the emptying operation of the conduit, in large quantities thanks to their large orifice. They cannot expel air if the system is pressurized.

• • Trifunctional or triple effect suction cups: They can carry out the expulsion and admission of air, and the expulsion of air with the pressurized installation and the water circulating through it. Generally, they consist of a body that contains a large float and a small float that is arranged next to the trap in a compact body, although they can also be found as two bodies connected to each other.

 

 

Where are they placed in the hydraulic installation?

Commonly, the points where the installation of suction cups should be studied are:

• The highest points of driving.
• Sections of the pipeline where there are changes in slope.
• Sections where there is a change of section in the pipe.
• After pressure reducing, anti-return and/or check valves.
• At points close to measuring devices.
• In the rectilinear sections, arrange them every 500-1000 meters.
• In general, in those points where there may be accumulation of air.

The type of suction cup and the position where it is installed in the hydraulic system depends on the amount of air to be evacuated.

All the monofunctional suction cups they are usually arranged at the pumping group outlet and at road junctions or fords; the bifunctional suction cups (admission - expulsion) are usually installed in long sections of uniform slope and, the trifunctional suction cups (purge-admission-expulsion) are generally placed at high points of the installation and at changes in slope in the pipes. Its use is recommended at high points to facilitate the maneuver of filling pipes, before the meters, filters and every 400 meters of pipes with a uniform slope.

Parameters to take into account for the installation of suction cups

When sizing a suction cup, it is necessary to know: the maximum pressure to be reached during the pipe filling process, the minimum pressure to be reached when the pipe is emptied and its working pressure, which will serve to determine the purger and the composition of the bifunctional suction cups.

 

In our web page you can find both suction cups from plastic and Ductile function, capable of withstanding higher pressures. Don't hesitate to get in contact contact us if you need more information or want to make an inquiry!