## The valve pressure class conversion of Mpa，LB，K，bar

PN, Class, K, bar are all units of pressure rating to express the nominal pressure rating for pipelines, valves, flanges, pipe fittings or fittings. The difference is that the pressure they represent corresponds to different reference temperatures. PN refers to the corresponding pressure at 120℃, while CLass refers to the corresponding pressure at 425.5℃. Therefore, the temperature should be taken into account in pressure conversion.

PN is mostly used in European standard systems such as DIN, EN, BS, ISO and Chinese standard system GB. Generally, the number behind “PN” is an integer number denoting pressure classes, approximately equivalent to normal temperature pressure Mpa. For valves with carbon steel bodies, PN refers to the maximum allowable working pressure when applied below 200℃; For cast iron body, it was maximum allowable working pressure when applied below 120℃; For stainless steel valve body, it was maximum allowable working pressure for service below 250℃. When operating temperature increases, meanwhile the valve body pressure decreases. Commonly used PN pressure range is (unit of Bar): PN2.5, PN6, PN10, PN16, PN25, PN40, PN63, PN100, PN160, PN250, PN320, PN400.

Class is the common valve pressure rating unit of the American system, such as Class150 or 150LB and 150#, which all belong to the American standard pressure rating, representing the pressure range of pipeline or valve. Class is the calculation result of the binding temperature and pressure of a certain metal according to ANSI B16.34 standard. The main reason pound classes do not correspond to nominal pressures is that their temperature benchmarks are different. The pressure of a gas is referred to as a “psi” or “Pounds per square inch”.

Japan mainly use the unit of K to indicate the pressure level. There is no strict correspondence between nominal pressure and pressure grade due to their different temperature reference. The approximate conversion between them is shown in the table below.

The conversion table between Class and Mpa

 Class 150 300 400 600 800 900 1500 2000 2500 Mpa 2.0 5.0 6.8 11.0 13.0 15.0 26.0 33.7 42.0 Pressure rating medium medium medium high high high high high high

The conversion table between Mpa and bar

 0.05(0.5) 0.1(1.0) 0.25(2.5) 0.4(4.0) 0.6(6.0) 0.8(8.0) 1.0(10.0) 1.6(16.0) 2.0(20.0) 2.5(25.0) 4.0(40.0) 5.0 (50.0) 6.3(63.3) 10.0(100.0) 15.0(150.0) 16.0(160.0) 20.0(200.0) 25.0(250.0) 28.0(280.0) 32.0(320.0) 42.0 (420.0) 50.0(500.0) 63.0(630.0) 80.0(800.0) 100.0(1000.0) 125.0(1250.0) 160.0(1600.0) 200.0(2000.0) 250.0(2500.0) 335.0(3350.0)

The conversion table between lb and K

 Lb 150 300 400 600 900 1500 2500 K 10 20 30 40 63 100 / Mpa 2 5 6.8 10 15 25 42.0

## Why the open and closure is difficult for large caliber globe valve?

Large diameter globe valves are mostly used for media with big pressure drop such as steam, water, etc. Engineers may face the situation, that the valve is often difficult to close tightly and prone to leakage, which is generally due to the valve body design and insufficient horizontal output torque (adults with different physical conditions have the horizontal limit output force of 60-90k). The flow direction of the globe valve is designed to be low-enter and high -exit. Manual pushes the handwheel to rotate so that the valve disc moves downward to close. At this time, the combination of three forces needs to be overcome:

1) Fa:  Axial jacking force;

2) Fb: Packing and stem friction;

3) Fc: Friction force Fc between the valve stem and disc core;

The sum of the torques∑M=(Fa+Fb+Fc)R

We can draw the conclusion that the larger the diameter is, the larger the axial jacking force is and the axial jacking force is almost close to the actual pressure of the pipe network when it is closed. For example, a DN200 globe valve is used for the steam pipe of 10bar, it only closes the axial thrust Fa=10×πr²==3140kg, and the horizontal circumferential force required for closing is close to the limit of the horizontal circumferential force output by the normal human body, so it is very difficult for a person to completely close the valve under this condition. It is recommended that this type of valve be reversely installed to solve the problem of difficult closing but produce the difficult-opening at the same time. Then there is a question, how to solve it?

1) It is recommended to choose bellows sealing globe valve to avoid the impact of friction resistance of the plunger valve and packing valve.

2) The valve core and valve seat must choose the material with good erosion resistance and wear performance, such as castellan carbide;

3) Double disc structure is recommended to avoid excessive erosion due to a small opening, which will affect the service life and sealing effect.

Why the large diameter globe valve is easy leakage?

The large-diameter globe valve is generally used in boiler outlet, main cylinder, main steam pipe and other parts, which are prone to produce the following problems:

1) The pressure difference at the outlet of the boiler and the steam flow rate are both large, both have great erosion damage on the sealing surface. In addition, the inadequate combustion of the boiler makes the steam at the outlet of the boiler water content is large, easy to damage the sealing surface of the valve such as cavitation and corrosion.

2）For the globe valve near the boiler outlet and cylinder, intermittent overheating phenomenon may be in the fresh steam during the process of its saturation if the boiler water softening treatment is not too good often precipitate part of  the acid and alkali substances, the sealing surface will cause corrosion and erosion; Some crystallizable substances may also adhere to the valve seal surface crystallization, resulting valve cannot be tightly sealed.

3) Due to the uneven amount of steam required by the production of valves at the inlet and outlet of the cylinder, evaporation and cavitation are easy to occur when the flow rate changes greatly, and damage to the sealing surface of the valve, such as erosion and cavitation.

4）The pipe with large diameter needs to be preheated, which can allow the steam with the small flow to be heated slowly and evenly to a certain extent before the globe valve can be fully opened, so as to avoid excessive expansion of the pipe with rapid heating and damage the connection. But the valve opening is often very small in this process, so that the erosion rate is far greater than the normal use effect, seriously reduce the service life of valve sealing surface.

## How many types of globe valve do you know?

The globe valve is designed with a stem that moves up and down to allow the medium flow one-way movement and make the sealing surface of the valve disc and seat tightly fit to prevent medium flow. It’s characterized saving elbow and operate conveniently and can be installed in the bent part of the pipeline system. There are various types of globe valve and designs, each with their own pros and cons. In this blog, we will introduce the classification of globe valves in details.

The flow direction of globe valve

1. Tee shape/Split body globe valve
The design making inlet and outlet channels of the valve are 180° in the same direction and has the lowest coefficient of flow and highest pressure drop. Tee/Split type globe valve can be used in severe throttling services such as in bypass line around a control valve.
2. Y pattern globe valve
Its disk and seat or the seat sealing an inlet/outlet passage present a certain angle, usually 45 or 90 degrees to the pipe axis. Its fluid hardly changes flow direction and has the least flow resistance in the globe valve types, suitable for coke and solid particles pipeline.

3. Angle pattern globe valves

Its flow inlet and outlet are not in the same direction with a 90° angle, which produces certain pressure drop. The angle globe valve is characterized by its convenience and without the use of an elbow and one extra weld.

Stem and disc of globe valves

1. Outside screw stem stop valve
The stem thread is outside of the body without connection with the medium to avoid the corrosion, easy to lubricate and operate.
2. Inside screw stem stop valve
The inner valve stem thread contact directly with the medium, easy to be corrosion and cannot be lubricated, usually used in the pipeline with the small nominal diameter and the medium working temperature is not high.
3. Plug disc globe valve

Plug valve is also known as the plunger globe valve. With a radial sealing structure design, by the polished plunger on the two elastic sealing ring through the body and bonnet connection bolt applied on the bonnet load around the elastic sealing ring to achieve the sealing of the valve.

4. Needle globe valve

Needle globe valve is a kind of small diameter instrument valve, which plays the role of opening and closing and flows control in instrument measuring pipeline system.

5. Bellows globe valve

Formed stainless steel bellows design offers reliable sealing performance, suitable for flammable, explosive, toxic and harmful media occasions, can effectively prevent leakage.

Applications of globe valves

1. PTFE-Lined globe valve
PTFE Lining globe valve is the valve that molding(or inset) Polytetrafluoroethylene resin in the inner wall of the metal valve pressure piece (the same method applies to all kinds of pressure vessels and pipe accessories lining) or the outer surface of the valve inner piece to resist the strong corrosive medium of the valve. PTFE lined globe valve is applicable to Aqua regia, sulfuric acid, hydrochloric acid and various organic acids, strong acids, strong oxidants at various concentrations of -50 ~ 150℃, as well as strong alkali organic solvent and other corrosive gases and liquid medium in the pipeline.
2. Cryogenic globe valve
Cryogenic globe valves usually refer to valves operating below -110℃. It is widely used in liquefied natural gas, petroleum and other low-temperature industries. At present, the globe valve with an applicable temperature of -196℃ can be manufactured, which uses liquid nitrogen for low-temperature pretreatment to completely avoid sealing deformation and leakage.

PERFECT manufacture and supply globe valves according to ANSI and API standards, the valve disc and seat sealing surface are made of stellite cobalt carbide surfacing that offering various advantages like reliable sealing, high hardness, wear resistance, high-temperature resistance, corrosion resistance, abrasion resistance and long service life. We design each valve according to the flow parameters presented. Contact our sales representative for details.

## A collection of API valve standards

In the United States institutions system, there are several standards can be used to specify the industrial valve like ASME standard ( American Society of Mechanical Engineers), API standard (American Petroleum Institute), ANSI standard (American National Standards Institute), MSS SP standard (Manufacturers Standardization Society of the Valve and Fittings Industry). Each of them has specific specifications for valves and complements each other, here we collect a series of commonly used valve API standards for general industrial valves.

 API 6A Specification for wellhead and Christmas tree equipment API 6D specification for pipelines and pipe valves API 6FA: The standard for Fire Test for Valves API 6FC Fire Test for Valve with Automatic Backseats. API 6FD Specification for fire test for check valves. API 6RS Referenced Standards for Committee 6, Standardization of Valves and Wellhead Equipment. API 11V6 Design of Continuous Flow Gas Lift Installations Using Injection Pressure Operated Valves. ANSI/API RP 11V7 Recommended Practice for Repair, Testing, and Setting Gas Lift Valves. API 14A Specification for subsurface safety valve equipment API 14B Design, installation, operation, test and redress of the subsurface safety valve system. API 14H Recommended practice for installation, maintenance and repair of surface safety valves and underwater safety valves offshore API 520-1 Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries: Part I – Sizing and Selection. API 520-2 Recommended Practice 520: Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries-Part II, Installation. API 526 Flanged Steel Pressure Relief Valves. API 527 Seat Tightness of Pressure Relief Valve. API 553 Refinery Control Valve API 574 Inspection of Piping, Tubing, Valves, and Fittings API 589 Fire test for the evaluation of valve stem packing API 591 Process valve qualification procedure API 594 Check valves: Flanged, lug, wafer and butt welding API 598 Valve Inspection and Testing. API 599 Metal Plug Valves – Flanged and Welding Ends API 600 Steel gate valves – Flanged and butt-welding ends, bolted bonnets API 602 Gate, globe, and check valves for size and DN100(NPS 4) and smaller for the petroleum and natural gas industries. API 603 Corrosion-resistant, Bolted Bonnet Gate Valves—Flanged and Butt-welding Ends API 607 Fire test for quarter-turn valves and valves equipped with nonmetallic seats API 608 Metal Ball Valves-Flanged, Threaded and Butt-Welding Ends API 609 Butterfly valves: Double flanged, lug and wafer type API 621 Reconditioning of Metallic Gate, Globe, and Check Valves

## Which actuator controller is better for valve? Electric or pneumatic?

Valve actuators refer to devices that provide linear or rotary movement of the valve, which using liquid, gas, electricity or other energy sources and converted it by motors, cylinders or other devices.

Pneumatic actuator uses air pressure to realize the valve drive open and close or regulation with one piece implementation and regulation mechanism, can be divided into the membrane, piston and rack and pinion pneumatic actuator. The pneumatic valve structure is simple, easy to operate and check, can also easily achieve the positive reaction of the exchange, more economical than electric and hydraulic. It is widely used in power plant, chemical industry, oil refining and other production processes with high safety requirements.

Electric actuator has a large torque, simple structure and easy to maintenance, can be used to control air, water, steam and corrosive media like mud, oil, liquid metal, radioactive media and other types of fluid flow. It also has good stability, constant thrust and good anti-deviation ability. Its control accuracy is higher than the pneumatic actuator and can well overcome the imbalance of medium, mainly used in power plants or nuclear power plants.

When selecting a valve actuator, it is necessary to know the type of valve, torque size and other issues. Generally in the term of the structure, reliability, cost, output torque and other terms to consider. Once the actuator type and the drive torque required for the valve are determined, the actuator manufacturer’s data sheet or software can be used for selection. Sometimes the speed and frequency of valve operation should be considered. Here we collect some tips or suggestion for the actuators  choices:

Cost
The pneumatic actuator must be used together with valve positioner and air source, and its cost is almost the same as the electric valve. In water and sewage treatment, most valve actuators are operated in on/off mode or manually. The monitoring functions of electric actuators, such as overtemperature monitoring, torque monitoring, conversion frequency and maintenance cycle, must be designed in the control and test system, which leads to a large number of line input and output. In addition to terminal position sensing and air source handling, pneumatic actuators do not require any monitoring and control functions.

Security
Electric valves are an electric power source, circuit board or motor failure prone to spark, generally used in the environmental requirements are not high occasions. Pneumatic actuators can be used for potentially explosive occasions, and it is worth noting that the valve or valve island should be installed outside the explosion area, the pneumatic actuators used in the explosion area should be driven by trachea.

The service life
The electric actuators are suitable for intermittent operation, but not for continuous closed-loop operation. Pneumatic actuators have excellent overload resistance and are maintenance-free, requiring no oil change or other lubrication, with a standard service life of up to one million switching cycles, which is longer than other valve actuators. In addition, pneumatic components with high vibration resistance, corrosion resistant, strong and durable, even not damage at a high temperature. Electric actuators consist of a large number of components and are relatively easy to damage.

Response speed
Electric actuators run slowly than pneumatic and hydraulic actuators, it takes a long time from the regulator output signal to response and movement to the corresponding position. There is a great loss of energy when the supplied energy is converted into motion. Firstly, the electric motor converts most of the energy into heat, and then it uses gears with a complex structure. Frequent regulation will easily cause the motor to overheat and generate thermal protection.

Essentially, the main difference between electric and pneumatic valves is the use of actuators and has nothing to do with the valve itself. Choose which actuator to use that depends on the operating conditions, such as a chemical application or explosion protection or wet environment where need pneumatic valve and an electric valve is ideal for large diameter piping system.

## What’s the advatages of PEEK valve seats?

PEEK (Polyetheretherketone) was developed by ICI (British chemical industry corporation) in 1978. Subsequently, it was also developed by DuPont, BASF, Mitsui optoelectronic co., LTD., VICTREX and Eltep (United States). As a kind of high-performance polymer material, PEEK is characterized by low creep variable, high elastic modulus, excellent wear resistance and corrosion resistance, chemical resistance, non-toxic, flame retardant, still maintain good performance even at high temperature/pressure and high humidity under the poor working conditions, can be used for high temperature and high-pressure valves, nuclear valves, pump compressor valve plates, piston rings, valve and the core of the sealing parts. Why PEEK valves are so popular that depends on PEEK’s excellent characteristics.

High temperature resistant
PEEK resin offers a high melting point (334℃) and glass transition temperature (143 ℃). Its continuous use temperature can be up to 260℃and load thermal transformation temperature of 30%GF or CF reinforced brand is up to 316℃.

Mechanical properties
PEEK raw material resin has good toughness and rigidity, and it has excellent fatigue resistance to alternating stress comparable to alloy materials.

Flame retardant: flammability of materials, which is specified in standards UL94, is the ability to maintain combustion after being ignited with high energy from oxygen and nitrogen mixtures. First, a vertical sample of a certain shape is ignited, and then measured the time taken by the material to automatically extinguish. PEEK test results are v-0, which is the optimal level of flame retardancy.

Stability: PEEK plastic materials have superior dimensional stability, which is important for some applications. The environmental conditions such as temperature and humidity have little impact on the size of PEEK parts which can meet the requirements of high dimensional accuracy.

1. PEEK plastic raw material has a small shrinkage in injection molding, which is beneficial to control the dimensional tolerance range of PEEK injection parts, making the dimensional accuracy of PEEK parts much higher than that of general plastics;
2. Small coefficient of thermal expansion. The size of PEEK parts changes little with the change of temperature (which may be caused by the change of ambient temperature or friction heating during operation).
3. Good dimensional stability. The dimensional stability of plastics refers to the dimensional stability of engineering plastics in the process of usage or storage. This dimensional change is mainly due to the increase of activation energy of polymer molecules caused by some degree of a crimp in the chain segment.
4. Outstanding thermal hydrolysis performance. PEEK is low in water absorption under high temperature and humidity. No obvious change in size caused by water absorption of common plastics like Nylon.

PEEK was developed in just two decades, has been widely used in oil and gas, aerospace, automotive manufacturing, electronics, medical and food processing and other fields. In the oil and gas industry, PEEK’s exceptional performance makes it ideal for use as a primary sealing part.

The PERFECT company manufactured and supplied industrial valve with PEEK soft seats and we strive to provide with high-quality, specialty valves as quickly and efficiently as possible. Whatever it is you are looking for, PERFECT will help you to find the appropriate product in the suitable application.