The Most Important Rubber Diaphragm Designs
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You might not be aware, but rubber diaphragms are an essential component for an assortment of applications.
They provide a superior seal for pumps, valves, regulators, actuators, hydro-accumulators, and many other parts. Not only are they versatile, but they also come in several different designs, with each of them containing its own specific pros and cons.
When choosing the right rubber diaphragm for your needs, you need to consider which design will be suitable for what you plan to use it for. For example, are you best to go with a dished diaphragm that is designed to stretch to its maximum height, or should you choose a more versatile design such as the rolling diaphragm?
If you’re not sure where to start, here is everything you need to know about the variety of rubber diaphragm designs that are available.
What are Rubber Diaphragms Used for?
Rubber diaphragms are used in a variety of different means, and the design plays a vital role in how the device functions. For example, a simple rubber diaphragm may be used in pressure switches where all that’s required is for it to turn from one position to the next. In other instances, like regulators, the diaphragm may be necessary to return to its starting place once a process is complete.
These items can also be used to reduce the instance of pressure spikes and maintain the flow of gas or fluids. Alternatively, a rubber diaphragm can be used in air compressors or fuel pumps to help dislodge a gas or liquid so it can be transported.
The key component is in the design of the rubber diaphragm. There is no one size fits all solution. Depending on what your specific needs will determine the right design for your rubber diaphragm.
What Type of Rubber Diaphragm Designs are Available?
Rubber diaphragms come in all shapes and sizes. They are also made of different materials to ensure they are suitable for the environment they’re used in. Below are some of the most common rubber diaphragm designs. If you need help choosing the right one for your needs, then make sure to get in touch with HEPAKO.
There are four main types of diaphragms:
· Flat Diaphragms
· Dished Diaphragms
· Rolling Diaphragms
· Convoluted Diaphragms
Figure 1: Flat Diaphragm, Dished Diaphragm, Rolling Diaphragm, Convoluted Diaphragm
Flat Diaphragms
This type of rubber diaphragm is flat and generally round in shape. But more complex shapes are also possible. They are typically cut from rubber rolls or sheets. In some cases, they feature a cloth insert. As both sides have the same effective area, pressure can be applied from either angle.
Over the years, HEPAKO developed outstanding experience in die-cutting different rubber materials with a special focus on tight tolerances. Die-cutting is a very cost-effective way to produce flat diaphragms even with complex shapes. Flat diaphragms are often made from EPDM, Silicone, FKM or FFKM in different Shore A hardnesses.
Flat diaphragms are ideal for methane plants, pumps, pressure regulators, or any other application requiring regulation or control. Despite their varied use, they are limited in their function due to their shorter stroke length. It’s possible to overcome this through a modification known as blousing. This helps provide the diaphragm with enough slack for stroking.
Figure 2: Typical Design of a Flat Diaphragm, Source: Simrit Catalogue, Edition 2004, p. 16.2f (Freudenberg Simrit KG)
Dished Diaphragms
Resembling something you’d eat cereal from, the dished diaphragm features walls that slope inward from the cylinder to the piston. This molded diaphragm design allows it to stretch to its maximum height in all directions while absorbing pressure with its double coat.
Like flat diaphragms, pressure can be applied from either angle. The effective diameter is dependent on the stroke.
Dished diaphragms are generally used with regulation equipment and actuators. They’re also perfect for dosing and measuring valves. However, it doesn’t provide complete movement and can have difficulty withstanding high pressures due to the sidewall slopes.
Figure 3: Typical Design of a Dished Diaphragm, Source: Simrit Catalogue, Edition 2004, p. 16.3 (Freudenberg Simrit KG)
Rolling Diaphragm
While a rolling diaphragm might resemble a deeper dish, its shape is closer to a top hat. This allows for a smoother rolling action as well as longer strokes. It also means the area receiving pressure will remain constant throughout the operation.
One of the benefits of this design is that it can be used with any lubrication. They also respond very well to minute pressure variations, which improves the performance relating to air and liquid pressure control fields.
It doesn’t matter if you’re using a rolling diaphragm for extremely low-pressure applications or high-pressure ones. The design is suitable for both and everything in between.
Figure 4: Typical Design of a Rolling Diaphragm, Source: Simrit Catalogue, Edition 2004, p. 16.3 (Freudenberg Simrit KG)
Convoluted Diaphragm
These types of diaphragms act as a flexible barrier between a stationary and moving part. This allows it to prevent any fluids from combining between the two chambers. Convoluted diaphragms have slightly greater stroke capabilities than flat diaphragms. If an application allows limited stroke heights, convoluted diaphragms allow to achieve an almost stroke-independent effective diameter.
The convoluted diaphragm is typically a rubber molded part that is molded into the same shape that it will take once it's assembled in the application. You can find convoluted diaphragms commonly made from a range of rubber materials, including convoluted diaphragms in EPDM, FKM convoluted diaphragms, chloroprene convoluted diaphragms, silicone rubber convoluted diaphragms, NBR convoluted diaphramgs and more.
Convoluted diaphragms are designed to ensure functions like regulation, dosing, control, measuring and more.
Figure 5: Typical Design of a Convoluted Diaphragm, Source: Simrit Catalogue, Edition 2004, p. 16.3 (Freudenberg Simrit KG)
Special types of diaphragms
Beside these main types, there are also some special types of diaphragms that we would like to present:
Drop Centre or Offset Convolution Diaphragms
A drop center diaphragm shares a close resemblance to the convoluted design. But there is a deeper center draw on these models. Thankfully, it includes all the same benefits as the convoluted diaphragm in addition to being easier to assemble and featuring a longer stroke capability.
They’re often used in the same functions as the convoluted diaphragm, such as regulation, control, and dosing. However, they’re best for applications with hardware limitations, such as the piston and flange being on the same plane.
Top Hat or Deep Draw Diaphragm
This type of diaphragm has great similarities to the rolling diaphragm and can be called a special type. The top hat design can be employed for the rubber diaphragm when a longer stroke is required from the application. This rubber diaphragm design is formed prior to assembly to ensure that it rolls the correct way before the operation commences.
There is a risk that the deep draw diaphragm can invert. Fortunately, there are methods to prevent this, such as using a certain type of piston as well as a curved lip retainer plate. It’s best to discuss with an expert before proceeding with this design to ensure it doesn’t impact the function of the application.
Double Taper Diaphragm
The deep draw design is also useful in other types of rubber diaphragms. The double taper is another example where the top hat style can reduce circumferential compression. The inclusion of an additional taper allows for the sidewall angle to be decreased.
This allows for the circumferential compression to be greatly reduced compared to other rubber diaphragm designs. It also improves the lifespan of the diaphragm, so you don’t need to replace it as regularly as other options.
What is Rubber to Metal Bonding?
It is possible to bond metal to rubber diaphragms during the molding process. While it requires an experienced manufacturer and needs some attention during the design stage, the process offers advantages both during the assembly and the operation of a pump.
The adhesive/ bonding agent used to connect the two components isn’t only dependent on the type of materials used. It’s also reliant on the use of the application and the interactions between the metal, rubber, and adhesive. For diaphragms, EPDM, FKM, Nitrile rubber (NBR), HNBR and silicone rubber are the most commonly used rubber materials bonded to metal. For each material, there is a special adhesive required. To go further into detail, you even have to consider the cross linking and the composition of each compound to select the right adhesive.
Thus, a lot of care and attention to detail is required to ensure the diaphragm functions as intended, and the adhesive holds whilst it’s in operation.
If you’re designing the metal component for the diaphragm, there are some factors to consider. For starters, you should avoid any sharp materials interacting with the rubber. Corners at the junction lines are also not recommended. You can also think about adding holes to the metal insert in order to strengthen the bond between rubber and metal in addition to the use of a bonding agent. It is also always important to design the inserts so that the part can be sealed during the vulcanization process in such a way that rubber cannot flow to undesirable places.
One other consideration is the type of metal you want to use. Steel is one of the most reliable materials to consider. However, brass, aluminium, stainless steel, and even nylon are common for rubber to metal bonding procedures. By the way, a bonding between plastics such as PEEK and rubber is also possible.
The benefit of considering rubber to metal bonding is that you can reduce assembly costs and operations. The final product is virtually ready for you to install. You don’t have to stress about any smaller parts like screws or rivets creating issues. There are also advantages in terms of longevity and performance.
HEPAKO has a long history of bonding different kind of rubber to metal. Get in touch with HEPAKO to discuss opportunities for your possible application.
What are Rubber Diaphragms Made from?
Once you’re clear on the type of rubber design you’re after, the next step is to choose the material the diaphragm should be made from. Different types of rubber are best suited to certain types of applications. It’s important to know the end application as precisely as possible in order to select the right rubber material.
Silicone Rubber (VMQ) / Liquid Silicone Rubber (LSR)
Silicone rubber is a material that’s not only resistant against heat up to 480 degrees Fahrenheit or 305 degrees Celsius, but it can withstand lower temperatures as low as -112 degrees Fahrenheit or -80 degrees Celsius.
Rubber diaphragms made from silicone rubber are most useful in the medical industry. However, they’re also resistant to ozone, aging, and extreme weather conditions, so they’re just as beneficial for applications that operate over a broad range of temperatures.
Detailed information about this material can be found here.
Fluoro Silicone Rubber (FVMQ)
If you need a rubber diaphragm that’s resistant to liquids like fuel or oil, then FVMQ could be a suitable material for you. The material combines the low-temperature flexibility of silicone with swelling resistance that fluoro rubbers are renowned for.
The temperature range isn’t as vast as silicone rubber, though. It can operate in conditions as low as -65 degrees Fahrenheit or -55 degrees Celsius to as hot as 390 degrees Fahrenheit or 200 degrees Celsius.
Chloroprene Rubber (CR)
A flame retardant option for your rubber diaphragm is chloroprene. It’s also resistant to weathering and ozone. Chloroprene rubber has good mechanical properties (tear resistance, elongation at break, tear strength), so it is considered very durable if you require a diaphragm that you don’t want to replace regularly.
This type of material is ideal for use in diaphragms and other applications that require weather resistance materials. However, it’s also a solid option for products that use oil, as chloroprene rubber can withstand the lasting effects of the liquid. Its temperature resistance ranges from -40 degrees Fahrenheit and Celsius to 210 degrees Fahrenheit or 100 degrees Celsius.
EPDM (Ethylene Propylene Diene Monomer Rubber)
Perhaps one of the most popular rubber diaphragm materials, EPDM features solid mechanical properties and strong resistance against UV rays, ozone, and weathering.
If your application uses hot or cold water, air, and steam, then EPDM is the right choice. It can withstand low temperatures from -22 degrees Fahrenheit or -30 degrees Celsius up to 266 degrees Fahrenheit or 130 degrees Celsius. For short periods, EPDM can also be applied in environments featuring temperatures of 340 degrees Fahrenheit or 170 degrees Celsius.
Detailed information about this material can be found here.
Fluoro Rubber and Fluro Carbon Rubber (FPM/FKM)
One of the other popular materials for rubber diaphragms is fluoro rubber. It might not be as flexible as other options that are available, but it is one of the best choices for high-temperature fluids and applications that need resistance against acids, chemicals, fuels, and oils.
It’s also got low gas permeability and can withstand temperatures as high as 430 degrees Fahrenheit or 220 degrees Celsius. Fluro rubber is also weatherproof and doesn’t get affected by exposure to ozone either.
FKM is often used in industrial, mechanical and even medical applications that interact with a variety of chemicals or extreme heat conditions.
Detailed information about this material can be found here.
Perfluoro Rubber (FFPM/FFKM)
Even though perfluoro rubber is quite expensive compared to other materials, it's compatible with a wide range of applications, including those that feature a high use of chemical ingredients. One disadvantage is that adhesives cannot be applied easily for the FFKM to metal bonding so that a mechanical bonding might be the best solution when going for FFKM. However, HEPAKO has built up experience over the years regarding the bonding of FFKM with metal.
Perfluoro rubber can also withstand temperatures up to 608 degrees Fahrenheit or 320 degrees Celsius. Almost every industry can utilize this rubber material for its diaphragms, courtesy of its flexibility and durability against chemicals and heat conditions.
Detailed information about this material can be found here.
Butyl Rubber (IIR)
Gas applications are best to feature rubber diaphragms made by butyl rubber. However, it’s also capable of withstanding chemicals such as acids too.
Industries that deal with adhesives, agricultural chemicals, and personal care tend to utilize butyl rubber for their rubber diaphragms. The high electric conductivity combined with the durability against chemicals and gases makes it the ideal choice.
Detailed information about this material can be found here.
Nitrile Rubber (NBR)
If fuel, oil or fat resistance is required, NBR is the material to go for. It can withstand heat as high as 230 degrees Fahrenheit or 110 degrees Celsius while also being compatible with oils, lubricants, and hydrocarbons.
Nitrile rubber is ideal for processes that involve hot oil as the diaphragm can operate in this environment without degrading. The major industrial consumers of NBR products are the automotive, motor vehicles and mechanical engineering sectors.
Detailed information about this material can be found here.
Hydrogenated Nitrile Butadiene Rubber (HNBR)
HNBR is also a good choice for a rubber diaphragm that will come into contact with a range of chemicals. This material is often the choice where gasoline, oil, kerosene, and turpentine are required during the application. It was developed to make up the mediocre heat resistance of regular NBR.
HNBR can operate in temperatures up to 300 degrees Fahrenheit or 150 degrees Celsius. The most common industries that use HNBR are oil fields and industrial settings. However, steel and paper mills are also known for using this type of material for their processes.
Who Can Help You Choose the Best Rubber Diaphragm Design?
The good news is that you don’t need to be an expert in the different types of rubber diaphragm designs and the various materials. HEPAKO can manufacture rubber diaphragms according to your specific requirements and provide advice on the best option to suit your needs.
If you need rubber diaphragms for your organization, then get in touch with HEPAKO today to discuss how we can help.
