Types of Valves

Usual practice is to use the terms safety valve or relief valve to indicate a relieving valve for system overpressure, and this will be generally followed here. When specific types of valves are significant, they will be emphasized. 

Types of Positive Pressure Relieving Devices (see manufacturers catalogs for design details) 

There are many design features and styles of safety relief valves, such as flanged ends, screwed ends, valves fitted internally for corrosive service, high temperature service, cryogenic service/low temperatures, with bonnet or without, nozzle entrance or orifice entrance, and resistance to discharge piping strains on body. Yet most of these variations have little, if anything to do with the actual performance to relieve overpressure in a system/vessel. 

A few designs are important to the system arrangement and relief performance  

The term Pressure-relief valve applies to relief valves, safety valves or safety-relief valves [10]. 

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Sepro Conta.iner, The Sepro container consists of a collapsible plastic bag fitted into a standard three-piece, tin-plated container such as a 202 X 214, 202 x 406, or 202 x 509 can. The product is placed within the bag, and the propellant is added through the bottom of the container, which is fitted with a one-way valve. There is no limitation on the viscosity of the product but compatibiUty with the plastic bag must be considered. A free-dowing hquid can be dispensed either as a stream or a fine spray, depending on the type of valve employed. A viscous material is often dispensed as a stream. This system has been used for caulking compounds, postfoaming gels, and depilatories. 

For any given appHcation of any type of valve, temperature, pressure, and corrosivity must be considered in the same manner as for the piping system itself. Valve vendors specify the temperature, pressure, and general service limitation for their valves and these are indicated in the manufacturers catalogs. 

Valve Problems. The primary solution to valve problems has been implantable replacement valves. The introduction of these devices necessitates open-heart surgery. There are two types of valves available tissue (porcine and bovine) and mechanical. The disadvantage of tissue valves is that these have a limited life of about seven years before they calcify, stiffen, and have to be replaced. The mechanical valves can last a lifetime, but require anticoagulant therapy. In some patients, anticoagulants may not be feasible or may be contraindicated. Of the valves which require replacement, 99% are mitral and aortic valves. The valves on the left side of the heart are under much greater pressure because the left ventricle is pumping blood out to the entire body, instead of only to the lungs. Occasionally, two valves are replaced in the same procedure. 

Pinch The industrial equivalent of controlling flow bv pinching a soda straw is the pinch valve, Mves of this tvpe use fabric-reinforced elastomer sleeves that completely isolate the process fluid from the metal parts in the valve. The valve is actuated bv applying air pressure directly to the outside of the sleeve, causing it to contract or pinch. Another method is to pinch the sleeve with a linear actuator with a specially attached foot. Pinch valves are used extensively for corrosive material service and erosive sliirrv senice. This type of valve is used in applications with pressure drops up to 10 bar (145 psi),... 

To achieve the more detailed improvements suggested here, it may be necessaiy to add a few questions to those asked during a norm HAZOP. For example, what types of valves, gaskets, and so forth, will be used ... 

The basic difference between this type of valve and the normal external loop sample valve is the incorporation of an extra port at the front of the valve. This port allows the injection of a sample by a syringe directly into the front of the sample loop. Position (A) shows the load position. Injection in the front port causes the sample to flow into the sample loop. The tip of the needle passes through the rotor seal and, on... 

Pilot-Operated Pressure Relief Valve - A pilot-operated pressure relief valve is one that has the major flow device combined with and controlled by a self-actuated auxiliary pressure reliefs valve. This type of valve does not utilize an external source of energy. 

Calculate individually the orifice area required to pass the flashed vapor component, using Equation (5a), (3b), (4), (5), or (6), as appropriate, according to service, type of valve and whether the back pressure is greater or less than the critical flow pressure. 

The various items of equipment in the production facility are connected hy valves, fittings, and piping to enable and control flow from one piece of equipment to another. Chapter 9 of Volume 1 discusses factors governing the choice of line size and wall thickness. This chapter describes the various types of valves and fittings commonly used in production facilities and presents some common piping details and specifications. 

It is good practice to use other types of valves for the first isolation valve, as shown in Figure 7-1. 

Valves have two main functions in a pipeline to control the amount of flow, or to stop the flow completely. There are many different types but the most commonly used are the gate valve and the globe valve. The gate valve contains a disk that slides at right angles to the flow direction. This type of valve is used primarily for on-off control of a liquid flow. Because small lateral adjustments of the disk cause e.xtreme changes in the flow cross-sectional area, this type of valve is not suitable for adjusting flow rates. 

From Reference [3], K values for straight-through valves, such as gate and ball (wide open), can also be calculated. These types of valves are not normally used to throttle flow, but are either open or closed. 

When properly designed, this type of valve arrangement conforms to the ASME code. It is a pilot operated pressure relief valve in which the major relieving device is combined with and is controlled by a self-activating auxiliary pressure relief valve. See Figures 7-5A and B. 

Code, Section S lII, and are tested at capacity by the National Board of Boiler and Pressure Vessel Inspectors. This type of valve characteristically pops full open and remains open as long as the overpressure exists. 

In eitfier case, the second step is to select the specific type of valve that meets the pressure and temperature requirements. 

This type of valve may be used when the variations in backpressure on the valve discharge connection do not exceed 10% of the valve set pressure, and provided this backpressure variation does not adversely affect the set pressure. 

The equivalent hole diameter for use in the equation for Z when considering the two types of valve trays studied here is given by ... 

Several types of valves used in compressor cylinders are shown in Figure 12-6. To function properly, a valve must seat uniformly and tighdy, yet must not have snap-action on opening or closing. Until pressure builds up to the discharge point, the valve must remain closed, open at dis-... 

The valve plates, discs, and springs are mounted in a valve cage, which is inserted in the cylinder. Valve breakage occurs due to fatigue of the metal or improper action. This requires replacement and an evaluation of the materials of construction as well as the basic type of valve. Each manufecturer presents his valve design to match his equipment. Only experience can determine which type of valve works best in a given application... 

Directional control valves may be classified in several ways. Some of the different ways are by the type of control, the number of ports in the valve housing, and the specific function that the valve performs. The most common method is by the type of valving element used in the construction of the valve. The most common types of valving elements are the ball, cone, sleeve, poppet, rotary spool, and sliding spool. The basic operating principles of the poppet, rotary spool, and sliding spool types are discussed in this text. 

Safety-Relief Valve this is an automatic pressure-relieving device actuated by the static pressure upstream of the valve and characterized by an adjustment to allow reclosure, either a pop or a non-pop action, and a nozzle type entrance and it reseats as pressure drops. It is used on steam, gas, vapor and liquid (with adjustments), and is probably the most general type of valve in petrochemical and chemical plants (Figures 7-3, 7-3A, and 7-4). Rated capacity is reached at 3% or 10% overpressure, depending upon code and/or process conditions. It is suitable for use either as a safety or a relief valve [1,10], It opens in proportion to increase in internal pressure. 

Apart from bottom blowdown valves (main BD valve), other types of valves are often employed. Blowdown valves also can be used to control high water levels, drain the boiler for cleaning or inspection purposes, and maintain chemical concentrations and water chemistry below maximum permitted levels. 

A type of valve located in the steam line and elsewhere that automatically cuts the boiler in and out, thus providing for online and offline operation. This valve protects the steam system in the event of a loss of pressure from a boiler, caused perhaps by a large steam leak. 

One of various types of valve employed to enable BD of a boiler. Main BD valves are located at the bottom of all boiler drums, shells, and headers. 

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