Diaphragm Valves vs Electrically Actuated Control Valves

What are Diaphragm Valves?

 

Diaphragm valves are named after a flexible disc that is connected with a platform at the top of the valve body, which in turn, forms a seal. A diaphragm is an adaptable component that responds to pressure and engages a force to open, close and control a valve.

 

Diaphragm valves use a durable diaphragm that is connected to the compressor by a stud, which is proceeded by being shaped into the diaphragm. The diaphragm is shoved, making contact with the bottom of the valve body, to shut-off as an alternative, instead of tweaking the liner closed to shut it off. Diaphragm valves are manually operated and are ideal to control the flow control by offering a variable and precise opening for handling pressure drop through the valve. A handwheel is turned until the desired amount of medium flow is transmitted throughout the system. The handwheel is in motion until the compressor pushes the diaphragm to counter the bottom of the valve body to either halt the flow or make way in the bottom until there is a passage for flow.

 

The diaphragm is secured to a compressor by a stud constructed inside the apparatus. The valve stem is moved up to start or enhance the flow in the compressor. To stop or reduce the flow, the compressor is modulated along with the diaphragm being thrust against the foot of the valves. Diaphragm valves are reliable for managing the flow of liquids containing solid matter and have the ability to be fixed in any position.

 

 

What are Electrically Actuated Control Valves?

 

There are two types of electric valve actuators; rotary and linear. Each of them uses special valves to function.

 

The motor varies in voltage and puts a lot of emphasis on torque generation. To avoid heat damage from excessive functions or override current draw, electric actuator motors come along with a sensor which marks an increase in temperature in the motor mechanisms. The sensor gives out a signal when the circuit needs to be opened when overheated. The circuit can be closed again when the motor reaches a moderate temperature.

 

Electric actuators are dependent on a gear train attached directly to the motor to boost the motor speed which navigates the speed of the device. You can change the output speed by installing a cycle length control variable.

 

 

Why are Electrically Actuated Control Valves better?

 

– You do not need an air supply. Air supply may not be available in many places and it is also hard to keep track on.

 

– Colder climates can cause compressed air systems to freeze or clog but the electrically actuated controlled valves have the ability to withstand these temperatures.

 

– They are cost effective.

HNBR seals – Pushing Boundaries for the Energy, Oil, & Gas Industry

HNBR Seals

When it comes to aggressive EOG  environments that require extreme reliability, longevity, and durability, one elastomer comes to mind: Hydrogenated Nitrile Butadiene Rubber (HNBR). HNBR is renowned for its durability and retention of properties after overtime exposure to external elements like heat, oil, and chemicals that tend to weaken the durability of rubber seals.

 

Properties of HNBR

 

Hydrogenated Nitrile Butadiene Rubber (HNBR), is a variant of nitrile rubber (NBR) that has been hydrogenated to give it enhanced mechanical characteristics and, help in increasing resistance to wear and tear. The properties of hydrogenated nitrile rubber (HNBR) depend upon the acrylonitrile content (ACN) and the degree of hydrogenation of the butadiene copolymer. The fluid and chemical resistance improves as the ACN content is increased. The preceding improvements to the material properties over that of nitrile rubber (NBR) include greater thermal stability (up to 149°C/300°F, with short periods at higher temperatures), broader chemical resistance, and greater tensile strength.

 

Benefits of HNBR over the standard Nitrile and Fluorocarbons

1. HNBR Seals have enhanced resistance to environments that are prone to ozone and weathering, industrial lubricants, amine-based corrosion inhibitors, sour gases (H2S), and hot water/steam (150°C).

2. Maximum operating temperature +56°F (180ºC) in oil +320°F (160ºC) in air.

3. Minimum operating temperature -25ºF (-26°C) special grades –50°F (-45°C)

4. Minimum operations are much more competitive compared to existing technologies and lead to cost reducing, technical parameters improving, also strength increasing, and the better and more qualitative product.

5. Excellent aliphatic (not aromatic) hydrocarbon resistance.

6. Fit for use in methanol and sour environments, (up to 5% Hydrogen Sulfide)

 

Application Advantages of HNBR Seals in the Energy, Oil, & Gas Industry

HNBR seals should be considered over standard Nitriles and Fluorocarbon seals in selected applications for the following advantages:

 

Improved High-temperature Resistance

 

HNBR seals have excellent oil and fuel resistance along with superior mechanical properties and can sustain higher operating temperatures; up to 356ºF when immersed in oil.  Based on the compound formulation, standard nitriles can endure a temperature ranging between 200° and 300°F. Fluorocarbons in hot water/steam tend to dissolve its mechanical properties.

 

Resistance to Sour Crude

 

Oil and gas that contains hydrogen sulfide (H2S) can cause a substantial decrease in tensile, elongation and hardness properties in standard nitrile
and fluorocarbon seals. Tests conducted have proved that HNBR seals promise stronger resistance over standard nitriles and fluorocarbon when directly in contact with heat, aggressive fluids, and corrosive chemicals.
Explosive Decompression Resistance

 

The compression-set resistance of HSN at high temperatures (such as 302°F) is much better than standard nitriles. Fluorocarbons show signs of compression at temperatures as low as 0°F.

 

Resistance to Corrosion Inhibitors

 

Corrosion inhibitors with standard nitriles and fluorocarbons create increased elongation, loss of elasticity and rigidity. On the other hand, HNBR seals have a higher resistance to a variety of common corrosion inhibitors.

 

Resistance to Explosive Decompression

 

Explosive decompression occurs when gas at high pressure permeates into the elastomer. Nitriles and fluorocarbons have shown lesser resistance to high-pressure CO2, as compared to HNBR.

 

Cost-Effective Bridge Between Nitrile Rubber (NBRs) and (per) Fluoroelastomers (FMKs)

 

HNBR elastomers offer optimum performance at a cost between nitrile rubber (NBRs) and (per) fluoroelastomers (FMKs). HNBR seals bridge the gap between the two elastomers in many areas of application where resistance to heat and aggressive media are required simultaneously.

 

HNBR seals boast of invaluable properties like high durability, tensile strength, and outstanding abrasion resistance that push the performance boundaries of elastomers in the aggressive EOG environment, therefore, giving impetus to the keep up with the continuous innovation in the Energy, Oil, & Gas Industry.

What is a Viton® (FKM) Gasket & What are its Applications?

Many of the most challenging sealing applications require a heavy-duty gasket that can perform exceptionally well in the harshest of conditions. Such applications often call for gaskets made from a family of fluoroelastomers called FKM. While Viton® is the generic name for FKM, it actually is a brand name of DuPont for its synthetic rubber and fluoropolymer elastomer.

 

What Exactly is FKM?

The FKM family of elastomers consist of copolymers or terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP), hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2) and perfluoromethylvinylether (PMVE). Since DuPont was the first company to really market this material, its brand name Viton® has become the most commonly associated name with FKM.

 

Majority of synthetic rubbers are composed of long chains of carbon and hydrogen atoms. These rubbers are prone to swelling upon exposure to oil and have a limited temperature range. What’s more, they break down over time with UV exposure (through sunlight).

 

When fluorine is added to synthetic rubbers, it bonds tightly to the carbon atoms and makes the compound more resistant to other compounds while providing tremendous flexibility. This changes the properties of the material and makes FKM the high-performance rubber compound that is crucial to many applications.

 

FKM is known for excellent resistance to heat, chemicals, concentrated acids, oils, and aggressive fuels.

 

Material Grades for Viton® Gaskets

On the basis of material composition and applications, FKM comes in a number of different material grades. Some of these are:

 

General Use Grades:

 

Viton® A

Viton® A dipolymers are polymerized from two monomers – vinylidene fluoride (VF2) and hexafluoropropylene (HFP). It is the most widely used Viton® gasket material and has applications as rubber seals for aerospace and automotive lubricants and fuels.

 

Viton® B

Viton® B is a terpolymer, i.e. polymerized from three monomers – vinylidene (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). This material is primarily used in chemical processing, power industries, and utilities.

 

Viton® F

Viton® F is also a terpolymer, polymerized from three monomers – vinyl fluoride (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). F types offer the best fluid resistance out of all other Viton® types. They are extremely useful in applications that require resistance to fuel permeation.

 

High-performance Grades:

 

Viton® GB and GBL

Viton GB and GBL are fluoroelastomer terpolymers that are polymerized from three monomers – vinyl fluoride (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). These fluoroelastomers use peroxide cure chemistry that leads to a superior resistance to acid, steam, and aggressive engine oils.

 

Viton® GLT

This fluoroelastomer is specially designed to retain the high heat and chemical resistance properties of general use Viton® grades while improving the low-temperature flexibility. Also, Viton® GLT offers an 8 to 12°C lower glass transition temperature, which is indicative of low-temperature performance in elastomer applications.

 

Key Properties of a Viton® Gasket

When it comes to gasket materials, good compression set resistance or the ability to spring back after the load is taken off is needed. Other desirable properties include a wide temperature range and good chemical resistance. FKM offers exceptional performance in all these regards.

 

FKM is graded as ‘HK’ as per the ASTM D2000 standard for classifying elastomers. Here, H indicates that the performance of an FKM Gasket deteriorates very little after prolonged exposure to temperatures of 250°C (480°F). FKM also works well in low-temperature conditions going as low as -40°C (-40°F).

 

Whereas, the K indicates the resistance to swelling. Since K is the lowest possible rating, it means that FKM swells less than almost all other elastomeric materials. FKM is also highly resistant to chemicals and can withstand ozone, typical automotive fuels, and hydrocarbon lubricating oils. However, FKM doesn’t give as great results against strong acids, alkalis, and ketones.

 

Applications of Viton® for Rubber Gaskets

Viton® gaskets were first used in the aerospace industry owing to their fuel resistance and low burning characteristics. Now, their application can be found in fluid power, automotive, appliance, and chemical industries. Moreover, with the introduction of FDA grades, the uses of FKM have been extended to the food processing and pharmaceutical industries as well.

 

Viton® Gaskets are highly recommended for harsh, high-temperature environments. They are often used with lubricating and fuel oils, gasoline, vegetable oils, alcohols, diluted acids, hydraulic oil, and kerosene because of their chemical resistance. In addition, Viton® applications can also be found in fuel seals, cap seals, T-seals, and radial lip seals in pumps. FKM gaskets also offer superior UV resistance that makes them a great choice in applications where prolonged sunlight exposure is expected.

 

We hope that you found this information useful. If you’re looking for FKM or Viton® gaskets for your application, Harkesh Rubber manufactures top-of-the-line products to fulfil your sealing needs. In fact, we can produce low-temperature FKM gaskets that can withstand up to -50°C! Simply contact us for your Viton® gaskets needs.

THE IMPORTANT FEATURES AND ROLES OF A ROLLING DIAPHRAGM

Diaphragm seals are found in industries that need maximum execution in severe environments, such as the automobile, aviation, pharmaceutical, and food and water-processing industries. Mechanical systems usually use hydraulic actuators which is one of the major factors in the applications. Rolling diaphragms are ductile fluid control tools that are used to secure a perfect seal in any system, involving a piston and cylinder. Made from a combination of elastomer and fabric, they are found inevery shape and size.

 

The bellofram rolling diaphragm is a pliable and durable seal that has a unique layout which allows proportionately long piston strokes while avoiding the sliding friction, throughout. Coming in the shape of a cone that has been cut, or top hat, the diaphragm is folded within itself when positioned so that, during the mechanism, it rolls and rotates repeatedly on the piston skirt and cylinder wall.

 

The rolling action is easy and trouble-free, completely omitting any sliding contact and diverging friction. The exterior flange is clamped to the cylinder in the middle, connected to the top of the piston, this shapes a faultless blockade, averting pressure loss and massive leakage. It all comes down on the substance and outline that has been chosen to function thoroughly with an applied pressure of 3000 pounds. The temperatures range from –120ºF to +600ºF. There are diaphragms that are accessible, with a high tolerance to oil, acids, alkalies, steam and other corrosive fluids.

 

Features of a Rolling Diaphragm

A couple of advantages of rolling diaphragms include precise, repeatable positioning, long stroke lengths, without a spring rate, that refers to pressure made by rubber trying to return to its moulded area.

 

– It is completely friction free.

– There is no breakaway friction or evasion to start the motion all over again, even after being in one position for a long time.

– The spring rate is constant and there is stability in the resistance that is applied for pressure throughout the stroke .

– Because of its high sensitivity, the diaphragm is easily responsiviations in pressure.

– There won’t be any leaks.

– It is so versatile that it can be equipped for a variety of pressures, temperatures, and liquids.

– The position is consistent along with pressures that are similar, despite the direction of the stroke.

 

Role of Diaphragms in Automotive

Air cylinders have piston and rod seal friction which can encounter a jerk at low speeds or pressures. These seals have low durability, which makes it harder to maintain a course without drift. These can be avoided by replacing them with rolling-diaphragm air cylinders, which don’t have dynamic seals that result in wear and tear, friction or leakage. Furthermore, a top-notch seal is attached around the piston that is held back from the sliding motion and in turn, gives a better seal that doesn’t leak and drain the actuator.

The Importance of Choosing The Right O-ring for Fluid Sealing Applications

O-rings are the most common tools used for fluid sealing applications. They prevent leakages in pumps, valves, connectors and cylinders. The economic and compact components of o-rings are capable of carrying out dynamic and static operations in hydraulic and pneumatic applications.

 

Selecting the right o-ring is important to ensure a flawless sealing solution. The smallest mistake while choosing an o-ring can not only cost the business a loss of capital but also a loss of the clients’ trust. Every little feature of the o-ring makes a significant contribution in the end sealing results.

 

Several criteria are applied in order to determine the right size of o-ring after the nominal groove dimensions have been finalized. The following basic principles are extremely important in order to maintain the integrity of the seal along with a longer durability:

 

 

1) Compression

 

An o-ring must have a bigger cross-section than the radial gap of the groove. This consumes its elastomeric properties to provide a basic sealing force. The compression applied depends on the type of application which can be dynamic, static or many more.

 

2) Stretch

 

Since o-rings are used in various kinds of applications, they comprise negative or positive tolerances. Hence, a minor permanent stretch is applied in general, whereas in rod applications a minor permanent interface is applied over the outer diameter. This helps in a snap fit that assists with the assembly.

 

3) Gland fill

 

Even though early compression applied offers a low-pressure sealing, to maintain a high-temperature sealing, an energized pressure is needed. The groove width needs to be sufficient to allocate the pressure in the groove. This ensures that the centre of the pressure energizes the seal. To allow different rates of thermal swelling and expansion of o-rings as the media goes into the solution inside the elastomer, the standard gland fills are below 85 per cent.

 

These principles can be applied to numerous scenarios wherever o-rings can be used. These can be pistons, rods, face seal grooves and other such applications. A variety of standards have been evolved to support in specifying sealing solutions for standard metalwork dimensions.

 

In the o-ring industry, the term ‘size reference’ is also known as ‘dash size’. These terms denote the size and tolerance applied to the o-ring. A basic understanding of the different sizes of the o-rings can help the engineer identify the seal that minimizes the machine requirements. This, in turn, will help minimize the costs of the entire process. Consider the designing of a hydraulic actuator along with a common system pressure and a minimum force required. Based on these basic criteria, the operative area according to the piston’s requirement can be determined. Also, the minimum cylinder bore diameter can be calculated with this.

 

 

Different Standards of O-rings

The British standards comprise of BS 1806 and BS 4518, which are related to the metric and nominal o-ring size. These standards provide engineers with the liberty to apply their tolerances to grooves. However, the BS 1806 applies low levels of pressure to smaller cross-section o-rings and does not offer a good quality sealing solution for rod seals and pistons. These standards work well for face seal groves.

 

The Society of Automotive Engineers, USA has AS 5857 and AS 4716 as the two standards for dynamic and static sealing solutions used for rod seals and pistons. These are the most widely used standards of all and they provide comprehensive tough hardware specifications when matched with the AS 568 o-rings.

 

According to theInternational Standard Organization, the standard ISO 3601 defines grooves in a comprehensive manner. Providentially, the AS 568, BS 1806 and ISO 3601 dash sizes for o-rings correlate together. If an engineer states a -224 o-ring, he will know that the component dimensions will be 1.734 X 0.139 inches used for a two-inch cylinder bore application.

 

Engineers need to obtain assistance from experienced o-ring designers or use an easily available selection software package for the application. An improper calculation of the o-ring size will result in leakages.

Cost Against Quality

 

The standard rubber formula includes a polymer which can vary. To cut down production costs, the manufacturers replace a certain amount of carbon black or simply force mineral fillers with cheap fillers like talc and kaolin. These materials offer the rubber the same amount of hardness but a lower price as compared to rubber formulated with expensive mineral filler or carbon black. Apart from the hardness factor, there are many other factors as well. Therefore it is important to choose a reputed manufacturer that meets tensile strength, hardness, chemical compatibility and other such factors.

 

O-ring, a common tool that helps in keeping equipment running, may not initially seem important. Using the right o-ring for your application requires a small investment which is extremely essential. This results in quality work and guaranteed profits in the long run.

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