A proportional valve is a simple mixing element. It is used in industrial automation and engineering applied to system for conveying bulk materials by means of an air flow, generally called pneumatic conveying systems. In this article we will have a closer look at what it is, its applications and the advantages of Vismec proportional valves for the conveying plastic granules.

Proportional valve: general operation

The name “proportional valve” comes from the fact that it is used to create a proportion between two different types of material. This name is improper in this field, because in engineering it is usually referred to as being a valve that is able to change the flow rate of different types of flows proportionally to the control signal received.

Thus, proportionality is understood as the relationship between the control signal which varies in a certain range of values, and the opening position which is variable in a certain range too. These devices find application in various sectors, including the automotive, aerospace, chemical and energy industries. In these areas, for example, they can be used to:

• control pressure and flow rate of fluids in hydraulic systems;
• ensure precise dosing of liquids in chemical processes and other processes;
• regulate the speed in automatic transmission systems of vehicles.

In the case of proportional valves used in pneumatic conveying, the proportion between two different materials is not achieved through a continuous variation of a valve body that continuously modulates two flows. It is, instead, achieved by the proportion between the conveying time of a first material and the conveying time of a second material.

Thus, the proportional valves produced by Vismec allow the alternating suction, in a specific proportion, of two different plastic materials through the action of an air flow.   For example, it may be a virgin polymer and a regrind polymer, or two primary materials. The proportion between the two is simply set by indicating the percentage of one material compared to the other.

The versatility and precision of proportional valves make them very useful in various applications where handling of two materials belonging to the same granule receiver is required. For this reason, they are an essential component of the Vismec feeding systems for plastics processing companies. 

As we will see, the valves that we design and integrate into products for conveying plastic granules have specific characteristics that make them extremely functional. However, let’s start from the beginning by briefly explaining how this type of device works in general.

The proportional valve for bulk materials operates by means of two shutters which are able to block the flow of granules and hermetically seal the duct, in response to a command or control setting. This command controls the alternating opening of the valve stems, making it possible to create a ratio between two materials arriving at the same bulk receiver.

As we have mentioned, in the case of Vismec proportional valves, the material in transit consists of polymer granules sucked alternately according to an adjustable proportion. Looking at their use in conveying polymers for plastic processing, let’s focus on the proportional valves designed by our company.

Advantages of Vismec proportional valves for conveying plastic granules

The Vismec proportional valve, installed before or in correspondence with the plastic granule receiver, allows two different types of plastic materials to be sucked in alternately thanks to an air flow produced by the same vacuum generator. The valve switches the vacuum from a main pipe to a secondary one.

From the point of view of the process control, it is sufficient to set the percentage of the second material to manage the entire process. Through the control, it is possible to vary the percentages of the two components to obtain a loading proportion. To increase homogeneity, the materials can be alternated several times during the same loading cycle.

Let’s have a look at the features that make VISMEC proportional valves unique on the market.

• The extremely clean one-piece precision-cast stainless steel design avoids the presence of stagnation areas. Therefore, the passage of granules is fluid and without interruptions or deposits. The stainless steel body greatly reduces wear due to abrasion caused by sliding granular materials.
• The inspection window is made of borsilicate glass that can withstand temperature changes and is wear-resistant to impacts of granules. The window has gaskets made of elastomers and noble polymers with high temperature resistance that are not in contact with the granules .
• The valve is controlled by a Vismec receiver and does not need a separate stand-alone control. Once the receiver has been properly parameterised, the valve is also adjusted accordingly, without the need for additional control points.
• The shut-off system consists of two stainless steel double-stage shutters, in which the first stage stops the granules and the second stage seals the pipe to enable the perfect transfer of vacuum into the second pipe. There are also moulded elastomer wear-resistant gaskets without frontal impact, to allow a perfect seal.
• The proportional valve is part of a pneumatic conveying system for polymer granules or for granules dehumidification and conveying. This plant is controlled by a system that uses the standard OPC UA protocol, allowing the automated management of processes with an advanced and intuitive human-machine interface. 

Let’s now see the advantages of the proportional valve.

• Simple adjustment. The device allows you an easy adjustment of two different materials to be used on the same polymer processing machine. This element is particularly useful when it comes to ensure an accurate proportion of materials in transit, as in the case of Vismec proportional valves.
• Wear-resistance. This type of valve is designed and manufactured to withstand wear and weather conditions. Consequently, it ensures a long operating life and reliable operation over time.
• Presence of control and signalling systems that facilitate the use of the device.
• Perfect closure of the valve and connecting components to avoid inefficiencies.

As we have seen, the Vismec proportional valves allow you to manage different functions and passages within the systems in a simple, rapid and automated way by a single control point. So, they allow companies that use them to simplify operations, optimise time and reduce consumption.

If you want to know in detail how they work and the other Vismec proposals for feeding and conveying plastic polymers, contact our team. We will be happy to evaluate with you the most suitable solutions for your company.