Any sealed system with liquid or gas moving inside is potentially dangerous. Temperature increases, chemical reactions, or a banal automation failure lead to voltage surges in the pipes.
This is where they come to the fore. safety valves, as the last line of defense for your equipment. As a manufacturer, we at UKSPAR face the fact every day that engineers and installers underestimate the role of these devices. So let's understand the process mechanics, physics and engineering nuances.
Why a safety valve is a mandatory element of pressurized systems
When the coolant in the circuit heats up, it inevitably expands. The pressure starts to rise at a catastrophic rate and the fluid needs somewhere to go.
A safety valve for heating or industrial mains solves this problem purely physically – it opens and releases excess medium to the outside. Without this protection element, the network will simply burst at its weakest point.
The cost of a mistake here is measured not only by the cost of damaged equipment, but also by the safety of people nearby. Regulatory documentation clearly regulates the presence of this node in any closed circuits.
The principle of operation of a safety valve
The operation of this protective device is based on a simple but reliable physical principle - the balance of forces between the pressure of the working medium and the force of the locking mechanism. The internal design of the product consists of several basic elements that work synchronously:
- The seat is a fixed part of the body that forms a passage for transporting the working medium.
- A spool (or gate) is a moving element that blocks the flow of liquid or steam by pressing tightly against the working surface.
- A spring or lever mechanism is a force component that creates the necessary force to hold the shutter in the closed position.
As soon as the internal pressure exceeds the set limit, the valve is triggered. The force of the medium acting on the spool becomes greater than the resistance of the spring. At this moment, the mechanism begins to compress, the valve rises above the seat, and the through hole opens. The excess mass is discharged in portions or completely.
When the system parameters return to normal values, the compression force returns the movable element to its place, the saddle closes again, and the device goes into standby mode.
Main types of safety valves
The UKSPAR catalog presents a variety of pipeline fittings, so the price of a high-quality safety valve may vary depending on its purpose, design, and materials.
Spring-loaded safety valves
This type of protective fittings is the most common due to its compactness, reliability and the possibility of installation in various spatial positions. The main working element here is a calibrated spring. It is it that determines at what level of load the mechanism will be triggered.
The compression force is adjusted using a special screw or sleeve. When the internal pressure exceeds the resistance force, the spring is compressed, opening the way for the working fluid to be discharged. Spring models are universal, they are actively used in heating systems, water supply, as well as on technological lines where steam, gas or aggressive liquids are transported.
Lever-loaded valves
In lever-load designs, the force pressing the spool against the seat is created by a lever mechanism and a load suspended from it. The closing force depends on the mass of the load and the length of the lever arm.
Such devices are characterized by high adjustment accuracy, since by shifting the load along the lever, the opening threshold can be precisely adjusted. They are used in stationary industrial facilities of high capacity.
Proportional and two-position valves
According to the nature of the opening of the shut-off element, valves are divided into proportional and two-position:
- Proportional devices raise the valve gradually as pressure builds up inside the system. They are ideal for water or other liquids where a smooth discharge is required without sudden hydrodynamic shocks.
- Two-position models operate almost instantly and open immediately to the full stroke of the spool when the critical point is reached. This logic is necessary in systems where the working medium is steam or compressed gases.
The choice between these types depends on the dynamics of the processes in the system. The correctly selected type of response ensures that the equipment is not subjected to additional loads during an emergency release of the substance.
Classification of safety valves by spool lift height
The height of the lifting of the closing element affects its throughput. Depending on the size of the stroke of the internal closing element, there are:
- Low-lift devices. In these models, the lifting height of the moving element is from 1/20 to 1/15 of the diameter of the saddle. They have the simplest possible design and are used mainly in systems with liquid working media, where instant evacuation of large volumes of mass is not required.
- Medium lift devices. Here the stroke of the valve is in the range of 1/10 to 1/6 of the diameter of the through hole. They are often installed on process lines with moderate discharge speed requirements.
- Full-lift devices. In such valves, the lifting height is 1/4 or more of the diameter of the saddle. Due to the large opening of the passage, they are able to instantly pass a huge volume of substance through them, which makes them indispensable for protecting systems with steam or compressed gases.
The choice depends on how quickly the system is prone to uncontrolled voltage increases.
Where to install the safety valve
There are several key locations on pipelines and in engineering nodes where the presence of this element is regulated by safety regulations:
- at the outlet from the boiler or water heater, to the first shut-off element;
- on steam and hot water pipelines;
- on tanks for compressed gases and liquids – to protect the container from overfilling;
- on compressor equipment, directly on the receiver or injection line;
- in closed heating circuits, where the safety valve compensates for the expansion of the coolant and is installed at the highest point of the circuit.
The main rule of installation is that there should be no shut-off valves between the valve and the pressure source that could theoretically be closed. Otherwise, the protection becomes meaningless.
How to choose a safety valve: pressure, diameter, medium
The right choice is an engineering task that does not tolerate compromises. You cannot take the first product off the shelf, focusing only on its appearance or connection diameter. A comprehensive analysis of the system parameters is required.
Selection by operating pressure
This is the basic parameter to which the built-in spring or lever of the device is adjusted. The safety valve should open when the system operating parameters are exceeded by a certain amount, which is usually from 10% to 15% of the nominal network pressure.
For example, if the standard operating pressure in the circuit is 6 bar, then the device is set to operate at 6.6-6.9 bar. This margin allows you to avoid false openings with minor fluctuations in the system.
Selection by connection diameter
The size of the inlet pipe of the device must clearly correspond to the calculated throughput, and not simply coincide with the diameter of the pipe on which the installation is carried out. Designers calculate this parameter based on the maximum volume of the medium that must be evacuated per unit of time in the event of an accident. Narrowing the passage will lead to the fact that the device will not be able to cope with the flow of liquid or steam, and an excessive increase in diameter increases the cost of the project and complicates installation work.
Connection can be sleeve or flange. The flange provides reliable tightness on large diameters and high pressure, withstands vibrations. Threading is faster in installation on small diameters, but requires high-quality sealing of threaded connections.
Choice by working environment
The properties of the substance transported by the pipeline directly affect the internal configuration of the fittings:
- for water and other liquids, devices with a smooth opening type are selected;
- for steam, compressed air or gas, models with high valve lift are required.
In addition, the chemical composition of the environment dictates the requirements for seals. For aggressive chemical compounds or high temperatures, special heat-resistant and chemically neutral materials are required.
Body materials: brass, cast iron, stainless steel
The body material determines the durability of the valve and its scope of application.
Brass is a lightweight, ductile and corrosion-resistant alloy. It is ideal for domestic heating systems, small boilers and water supply networks. Brass products are not afraid of contact with water and are affordable.
Cast iron is a traditional material for industry and large-diameter main networks. Cast iron bodies are characterized by high strength, durability and the ability to work in difficult conditions.
Stainless steel – has absolute resistance to aggressive chemicals, high temperatures and corrosion processes. Stainless steel fittings are installed in food, pharmaceutical and chemical industries, where increased requirements for cleanliness and reliability are imposed.
Typical mistakes when choosing and installing
Even if you buy a safety valve of the highest quality, it will not be able to protect the system if gross errors are made during selection or installation. Among the most common:
- Installing a shut-off valve between the valve and the system. Never do this, as human error can lead to accidental closing of the protection line. Then the pressure relief valve will not operate.
- Incorrect installation direction. Each product has an arrow on the body that indicates the direction of the medium flow. Installing the device backwards completely blocks its operation.
- No drain line. The valve outlet should not just hang in the air. It should be connected to a pipe to drain hot water or steam to a safe location.
Like any mechanism, the valve needs inspection. It is recommended to perform a forced opening every six months to make sure that the spool is not "stuck" to the seat. Careful inspection is the only way to guarantee the safety of the engineering system.
By purchasing equipment from the trusted manufacturer UKSPAR, you receive not only reliable fittings, but also professional technical support. It will allow you to avoid annoying mistakes and ensure the smooth operation of your facility for many years.
