Pressure control valves have practical applications in every pneumatic and hydraulic system. To prevent damage to the hydraulic system, power wastage, and overheating of the hydraulic fluid, circuit designers use a variety of efficiently designed pressure control valves to regulate maximum system pressure and pump flow during non-action periods. Most of such valves are easy to install without consuming much space because they are smaller in size. Some pressure control valves are capable of relieving the pressure from the system, while others are good at maintaining the pressure within a certain limit. This article highlights Different Types of Pressure Control Valves:
There are many Different Types of Pressure Control Valves, we will discuss only major one in below.
1. Pressure Relief Valve
A pressure relief valve (PRV), also called a relief valve, is a pressure control valve used to regulate or restrict the pressure in a system. The pressure may build-up, which can lead to a process, instrument, or equipment failure. Pressure relief valves make it possible to avoid this disaster. They act as a shield that limits maximum pressure in a system by detracting the excess fluid when the pressure gets too high. As fluid is diverted, the pressure inside the vessel will stops rising and begin to drop. The valve will close once the pressure drops to the valve’s reseating pressure. The pressure relief valve is built or designed to open at a predetermined set pressure to defend pressure vessels and other instruments from being subjected to pressures that are higher than their design limits. The difference between the set pressure and reseating pressure is called blowdown. The blowdown of some pressure relief valves varies from 2–20%, while some valves have adjustable blowdowns.
The basic goal of a pressure relief valve is the protection of life and property by discharging fluid from an over pressurized vessel. They should be prepared for operating at all times, especially during the time of power failure and crisis when system controls are nonfunctional. Two categories of relief valves are closing valves that include spring-loaded and pilot-operated valves; the second is non-recurring valves that include rupture disks and buckling pins. A spring-loaded pressure relief valve consists of inlet nozzle, valve seat, valve body, seat holder, bonnet, cap, spring, seal and set pressure adjusting screw.
2. Pressure Reducing Valve
Pressure Reducing Valve is an automatic control valve organized to reduce high unregulated inlet pressure to constant, reduced outlet pressure. Sometimes, it is also indicated as pressure reducing regulator. It is a self-operated system used to lower excess pressure in a system. These valves are fully automatic and do not require power from an external source. Commonly, they have applications in the gas, steam, oil, and gas industry. The pressure reducing regulators are highly reliable and easily maintainable. Based on the mechanism of controlling the valve opening, they can be categorized as direct-acting and pilot-operated pressure-reducing valves. Direct-acting valves are compact, cheap, and easy to install. Plus, they are best for small loads. In comparison, the pilot-operated valve is ideal for big loads where precise pressure control is necessary. They are expensive and larger in size.
Pressure reducing valves can be utilized as bypass valves to save the system from power failure. Furthermore, under defined conditions, these valves can be used for water hammer protection. Such valves have the capability to act instantly by sensing and adjusting according to downstream pressure.
3. Sequence Valve
The sequence valve diverts the flow of fluids in a predetermined sequence. They are pressure-actuated valves, which resemble pressure relief valves in construction and operation principles. A sequence valve enables the pressurized fluid to stream to a secondary circuit only after an operation has been achieved and satisfied in the primary circuit. When closed, it lets fluid flow freely to the primary circuit to accomplish its first operation until the valve’s pressure setting is reached. Occasionally, it is needed to slow down the switching sequence for functional purposes. In this case, the operation of the sequence valve is not pressure-dependent; rather, it is operated by the adjustable stroke of a control piston.
The fundamental function of a sequence valve is to govern the sequential operation of multiple actuators. This function is important in many different industrial systems, involving aerospace, automobiles, fluid processing, and more. Sequence valves often possess check valves, which allow reverse flow from the secondary circuit to the primary circuit. Nonetheless, sequencing action is delivered only when the flow is from the primary to the secondary circuit.
4. Counterbalance Valves
The counterbalance valve is also known as the load holding valve because it prevents the load from falling by maintaining the backpressure. It permits the fluid to flow in one direction only while restricting the flow in another direction. They are used with cylinders to carry the suspending load and handle with overload safely. The counterbalance valves have two ports; the primary port is joined to the rod end of the cylinder, while the secondary port is connected to the directional control valve. When pressurized fluid streams to the cylinder’s cap end, it extends and raises the pressure in the rod end that shifts the main spool in the valve. This establishes a path for the fluid to pass through the secondary port to control the valve and reservoir.
Counterbalance valves provide safety by automatically managing the descent of load. It can also be used in hydraulic motors. The design is quite simple, which allows for multiple variations to satisfy personal preferences. However, if a counterbalance valve gets stuck in the open position, it may result in significant instability, which leads to equipment failure.
5. Unloading valve
The 5th number in Different Types of Pressure Control Valves is unloading valve that operates the pump at a minimum load. These valves decrease the heat and preserve energy by draining the extra fluid to the tank when the flow is not required. The port of the unloading valve is connected to the pipeline that is to be unloaded. The pilot port detects the pressure of the system, and when the set pressure is reached, it sends a signal to initiate unloading.
Pressure regulators come in a variety of forms. The precision and the stability of the regulated pressure achieved can vary greatly with the type and design of each. When looking for the right regulator for a specific application, consideration of the form, precision and stability should be understood. The following is a short explanation of what pressure regulators are and how they differ in complexity.
What is a Pressure Regulator?
Pressure regulators are mechanical valves that use feedback to control pressure in both pneumatic and hydraulic systems. There are basically two types of regulators: one regulates upstream pressure (back-pressure regulators) and the other regulates downstream pressure (pressure-reducing regulators). The pressure is usually contained in a system where fluid is flowing from one place to another through pipes into storage tanks or pressure vessels. A regulator is used to adjust the upstream or downstream pressure from the point where the regulator has been inserted within the system.
They can be as simple as a manually controlled valve to a complex, automated precision system with a pressure sensing element in a feedback loop. The feedback comes from the pressure that is being regulated and this feedback controls the regulator output, either mechanically or electronically. Mechanical feedback is accomplished using a spring-loaded or pressure-controlled diaphragm, bellows or piston, which controls a valve that acts to increase or decrease the flow through the regulator based on the pressure being regulated. This mechanical regulation of flow acts to control the pressure. In an electronic regulator, the input from a pressure transmitter is used to adjust a valve or valves that control the pressure.
For the purpose of this post, we will concentrate on pressure-reducing regulators. These regulators reduce a relatively high incoming pressure to a lower outgoing pressure in order to protect sensitive components downstream, or to precisely control a pressure-sensitive process or measurement. Fluid dynamics is a complex subject and tells us that a fluid flowing through a restriction loses energy; pressure-reducing regulators take advantage of this property to regulate pressure. Pressure in any system is defined as the force per unit area within that enclosed system. Pressure is influenced by the quantity of the fluid present (number of molecules), the volume in which it is contained, and the fluid temperature. Most pressure regulators work to control the number of molecules that are allowed to enter (or exit) the system and thus control the system pressure. Another type, briefly discussed below, is a regulator that controls pressure by increasing the force applied to a closed system.
What are the various types of Pressure Regulators?
A distinction in the classification and understanding of regulator types can be made between mechanical "industrial regulators" and electronic "precision pressure regulators," which are also called “precision pressure controllers.” The latter is typically used within precision pressure calibrators. In either case, the same goal of pressure regulation is accomplished and the only difference is the degree of precision and stability achieved. For the purpose of this discussion, we will make this distinction as follows:
Industrial Pressure Regulation
An industrial pressure-reducing regulator incorporates a valve that is controlled by a spring-loaded diaphragm, bellows, or piston. The downstream pressure works to push the diaphragm or piston in a way that will permit or restrict the flow through the valve from the upstream to the downstream side of the valve. The spring tension can be adjusted so the downstream pressure maintains a pre-determined set pressure. Changes in the downstream pressure will automatically adjust the valve to allow or restrict the flow of fluid to achieve the setpoint. These industrial pressure regulators come in a variety of configurations, depending on the manufacturer. They are the preferred choice in industrial settings because they are robust and self-regulating, which uses the pressure of the system without the need for power input or external sensing elements. They can be set, left alone and the precision of the pressure control is adequate for most applications. Variations on this design can utilize two valves to help ensure proper regulation in all conditions.
Precision Pressure Regulation
Solenoid Valve Regulators
Another method of pressure regulation, often used within precision pressure controllers in calibration labs, utilize inlet solenoid (electro-mechanical) valves that allow a source pressure to enter the system and outlet solenoid valves to exhaust to atmospheric pressure or a vacuum. The downstream section of a system is controlled by adding or subtracting molecules of gas. Feedback from a downstream pressure sensor is measured and processed using a control algorithm that opens and closes the solenoid valves to produce the desired pressure setpoint downstream of the valves. To achieve a very precise controlled pressure, several inlet/outlet valves can be used in tandem that have fine to coarse orifices which can be opened or closed depending on the difference between a setpoint and the downstream pressure and/or the rate at which the pressure is approaching the setpoint. In this type of regulator, an extremely precise pressure can be achieved. The service life of these solenoid valves is affected by the pressure differential applied across the valve. It is for this reason Mensor uses a proprietary system that maintains a nominal differential across these valves to increase their longevity. Both the Mensor CPC4000 and CPC6050 incorporate this technology in order to provide years of operation with minimal solenoid failure. Solenoid valves are used in a variety of applications and are common in precision control systems. They are also relatively less expensive than their needle valve counterpart.
Needle Valve Regulators
Another regulation method uses two precisely machined needle valves made of a durable ceramic material using a small port and a threaded needle plunger. One valve supplies pressure and the other exhausts pressure from the controlled downstream system. The valves are designed to achieve both fast control and precise control. Valve modulation is controlled using an algorithm that constantly monitors the difference between the downstream pressure, the setpoint, and the rate at which the pressure is approaching the setpoint. The algorithm controls the needle valves to achieve a precision ramp into the setpoint and constant stability. This type of regulator achieves a high degree of stability in the pressure output which can be affected by temperature changes in the system or any fluctuation downstream. The Mensor CPC8000 uses this method which enables the product to deliver a precise, stable control at pressures up to 6000 psi.
Piston Actuated Regulators
Typically used in hydraulic systems, piston actuated regulators work similarly to deadweight testers by applying a force over a cross-sectional area of a piston within a cylinder. The pressure is equal to the force divided by the area of the piston, which is the definition of pressure, P=F/A. The greater the force applied, the greater the pressure. The Mensor CPC8000-H uses this method to precisely control pressures up to 23,000 psi. The benefit of this type of regulator is its ability to reach very high pressures, which is achieved by reducing the cross-sectional area of the piston.
Conclusion
There are many types of regulators. The term regulator is used across the spectrum from coarse to fine control of pressure. In calibration labs, components that achieve precise pressure regulation are sometimes called pressure controllers or calibrators. These precision pressure controllers rely on high accuracy pressure sensors and control algorithms to adjust the pressure to desired setpoints and to maintain stable control for the calibration of other pressure sensing components.
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