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Diaphragm pump is a positive displacement pump, which uses a displacement chamber or contraction and expansion chamber to move fluid through a flexible or reciprocating diaphragm.

The basic diaphragm pump consists of a diaphragm, a displacement chamber, a drive mechanism and two valves, although current industrial diaphragm pumps may use multiple chambers and multiple diaphragms.

The diaphragm is composed of a flexible or elastic material, which is fixed between the connecting flange and the displacement chamber containing the fluid, or between the displacement chamber and the auxiliary chamber containing the driving fluid (such as hydraulic oil or air).

The displacement chamber has two check valves designed to allow inflow from the inlet and outflow from the outlet. These check valves are flapper valves or spring-loaded ball valves, usually made of the same material as the diaphragm.

Diaphragm pumps use a driving mechanism (such as hydraulic fluid, air pressure, reciprocating pistons or solenoids) to bend the diaphragm to push the fluid out of the displacement chamber.

When the diaphragm is bent, it will cause the pressure in the chamber to increase and decrease alternately, thereby moving the medium in and out of the diaphragm pump.

Due to the high reliability of diaphragm pumps compared to alternative pump types, the use of diaphragm pumps continues to increase. Diaphragm pumps contain relatively few moving parts, no shafts or bearings that need to be sealed with the medium, and no sliding contact parts.

The diaphragm pump does not need to use sealing oil or lubricating oil, which means that there is no risk of oil vapor leakage and contamination of the pumped medium. In addition, because they do not use oil, they are usually unsealed, which helps to minimize cleaning requirements and maintenance downtime.

Figure 1. Schematic diagram of a mechanically driven diaphragm pump. Image source: NASA

Diaphragm pumps can transport liquids, gases, slurries or gas-liquid mixtures through reciprocating diaphragms, but the material chosen for the diaphragm material must be inert to the medium being pumped-or at least chemically resistant.

Diaphragm pumps can transport thin to highly viscous media. Even abrasive slurries can minimize the problem because the diaphragm isolates the media from the internal mechanism of the pump.

These factors help diaphragm pumps to become key process tools in paint, coatings, pigments, colorants, food, beverages, chemicals, adhesives, pharmaceuticals, wastewater and biological materials (such as blood, plasma and cells) industries.

A better understanding of the performance requirements and stresses of the diaphragm helps to select the best material to improve the reliability, effectiveness and life of the pump.

Diaphragm membranes usually need to withstand millions to tens of millions of deflection cycles, so materials with long deflection life are the key to ensuring predictable performance. This allows users to better plan for regular maintenance shutdowns and eventual membrane replacements.

The use of diaphragm materials with a short deflection life can cause pump failures, which can lead to costly unplanned shutdowns.

Pump failure may cause a series of problems downstream of the production plant.

For example, a sudden loss of fluid flow can damage valuable capital equipment in chemical processing plants, paper mills, pharmaceutical plants, power generation facilities, and semiconductor wafer manufacturing sites. It is also possible to lose a complete production batch.

Repairing or replacing highly specialized production equipment may take days or even weeks, leading to further production losses.

The long life and high durability of CHEMFILM® flexible barrier materials have been found to extend the average time between required maintenance cycles, thereby reducing the need for unplanned downtime.

Ensuring reduced pulsation and smooth flow are key factors in certain diaphragm pump applications, such as the precise dispensing and metering of paints, adhesives, dyes, lubricants, or active pharmaceutical ingredients.

Many pump OEMs recommend the use of pulsation dampers to better manage pulsation and surge. By increasing the number of smaller displacement diaphragm bending cycles per unit time, the pulsation intensity can be reduced and a more continuous flow can be obtained.

Figure 2. Materials with higher deflection life can increase the frequency of diaphragm deflection in (b.). Compared with the low-frequency bending cycle in (a.), it can reduce pulsation to provide a smoother flow. Image source: IEEE GlobalSpec

However, it is important to note that the increase in the number of bending cycles requires the use of materials with higher bending life performance characteristics than traditional diaphragm materials.

The electric diaphragm pump uses a small motor and a cam device to reciprocate the piston and bend the diaphragm.

Therefore, these devices can generate higher circulation and reduce pulsation compared to pumps driven by pneumatic or hydraulic fluid. These applications can benefit greatly from the installation of high flex life diaphragm barriers.

When using a production line that runs a series of chemicals, paints, pigments, or drugs on the same production line, it is important to consider the easy-to-clean and non-stick characteristics of the pump.

These lines must be cleaned of media or cleaned to prevent cross contamination.

Using Flex Barriers with low surface energy can prevent media adhesion or chemical bonding, allowing users to adopt more effective in-situ cleaning procedures.

Flex Barriers provide high smoothness, coupled with a crack-free and void-free surface, to ensure more direct and faster maintenance, because the surface unevenness (cavities or protrusions) is less, dust or media may be trapped or otherwise Ways to pile up.

Increasing the smoothness of the material will also reduce the coefficient of friction and further improve the cleanliness and flow of the pump.

Abrasion resistance is the key to pumping pastes, slurries, greases or pigments filled resins or paints. It is also important that the diaphragm material has excellent chemical resistance to acidic, alkaline and solvent media.

When choosing a suitable flexible barrier for the pump diaphragm, permeability should be considered. Depending on the thickness, density, or chemical nature of the flexible membrane, steam may permeate or otherwise pass through the pump diaphragm.

The corrosive or toxic chemicals dissolved in the medium may leak into the hydraulic system or the surrounding air, posing a considerable risk to personnel and equipment.

According to the EPA Leak Detection and Maintenance (LDAR) guidelines, diaphragm pumps and diaphragm valves are considered "leak-free".

Figure 3. Compared with traditional PTFE, the flexural life performance of CHEMFILM® Flex-Barrier material has been improved. Image Credit: Saint-Gobain Films and Fabrics

However, if volatile organic compounds (VOC) or steam successfully enter the atmosphere outside the pump, expensive maintenance measures may be required. If the diaphragm's poor flex life causes it to rupture prematurely, the diaphragm may cause leakage.

There is a risk of a highly permeable diaphragm material that allows water vapor to pass through it, or it may allow pollutants from the environment to enter the pumped medium. Water or steam present in pneumatic systems or hydraulic fluids may pass through the membrane and cause contamination of the process media.

Flexible barrier materials with low permeability and low mean time between failures are still viable options to prevent media release into the environment or vice versa.

The flexible barrier should comply with sanitary regulations and sanitary standards. This is especially important for diaphragms used in pharmaceutical, dental, medical and electronic equipment.

Diaphragms used for food and beverages need to comply with 21 CFR 177 standards of the US Food and Drug Administration, while diaphragms used for drugs or active pharmaceutical ingredients need to comply with United States Pharmacopeia Convention (USP) Class VI standards.

It is especially challenging to manufacture flexible barrier or pump diaphragm materials that provide the best combination of low permeability, high bending life, low friction surface energy, and proper regulatory compliance.

CHEMFILM® Flex Barrier materials are composed of a series of films and laminated structures produced using high-quality, high-molecular-weight fluoropolymer resins.

CHEMFILM® is the ideal solution for chemical process applications such as pump diaphragms, tank linings, valve diaphragms and check valve flaps.

These applications usually require fast transportation and high cycles, as well as a wide operating temperature range, chemical resistance, and stress crack resistance.

Figure 4. CHEMFILM® flexible barrier layer with PFA barrier layer has improved permeability. Image Credit: Saint-Gobain Films and Fabrics

CHEMFILM® materials can meet and often exceed the industry's requirements for fluorocarbon resin sheets and films. They also comply with ASTM D-3368 and other specifications.

Saint-Gobain uses a special surface treatment and a proprietary lamination process to ensure that CHEMFILM® Flex Barriers have low permeability, high bending life, high smoothness and low coefficient of friction.

The use of appropriately processed high molecular weight fluoropolymers, such as polytetrafluoroethylene (PTFE) and perfluoroalkoxy (PFA) copolymer resins, can ensure excellent stress crack resistance and extended flex life.

The low surface energy of fluoropolymers also has excellent anti-stick properties and extremely high chemical resistance, even when using highly aggressive chemical media.

CHEMFILM® materials have an operating temperature range of -425 °F to 500 °F (-254 °C to 260 °C), which means they can be effectively used in low and high temperature applications.

Figure 3 shows in detail that CHEMFILM® material has a higher bending life compared to traditional modified PTFE.

In this example, when tested using the internal high frequency bending life test of Saint-Gobain Specialty Film, the service life of CHEMFILM® products increased by approximately 70%. These tests are designed to simulate the bending life performance of diaphragm materials.

CHEMFILM® Flex Barriers show almost universal resistance to highly corrosive media and chemicals such as aromatic or chlorinated hydrocarbons, caustic alkalis, acids, ketones and acetates.

The resin used in the production of CHEMILM® Flex Barrier material complies with key regulations related to pharmaceutical, food and beverage, sanitary and medical applications.

These include FDA 21 CFR 177.1550, (EC) No. 1935/2004, (EU) No. 10/2011, (EC) No. 23/2006 (GMP), USP Class VI and 3-A sanitary standards.

CHEMFILM® materials also comply with REACH ((EC) No. 1907/2006) and RoHS (2011/65/EU) regulations, confirming that they do not contain any hazardous or prohibited compounds that may restrict the materials used in electronic products.

There are significant differences in the permeability of PTFE materials, and its performance largely depends on selecting the best material grade and ensuring the correct flexible barrier structure.

CHEMFILM® Flex Barrier (LP01) offers higher permeability than traditional modified PTFE materials, but the use of an additional PFA barrier provides the potential to alleviate this problem, reducing permeability by 30%.

Saint-Gobain Specialty Films works closely with its customers to meet the requirements of specific applications.

The company's experienced engineers continue to develop CHEMFILM® Flex Barriers to improve their permeability and bending properties. The combination of these two characteristics is the key to achieving a longer life under very harsh conditions.

Using CHEMFILM® Flex Barriers in a new diaphragm pump design or upgrading to an existing pump can significantly reduce the total cost of ownership for the user.

CHEMFILM® Flex Barrier material provides a longer diaphragm life than other materials, thereby reducing the number of downtimes required to maintain or replace the diaphragm.

Figure 5. Using CHEMFILM® flexible barriers in new diaphragm pump designs or upgrading existing pumps can minimize the total cost of ownership. Image source: IEEE GlobalSpec

The reduction in downtime requirements also reduces the cost of consumables due to the reduced need for spare parts or replacement diaphragms.

The low friction and high smoothness of the CHEMFILM® diaphragm surface facilitates direct cleaning between process runs of different chemical, paint, food or pharmaceutical ingredients.

Due to the reduced risk of contamination, the high cleanliness and higher durability provided by CHEMFILM® improves the quality of the media.

The robustness, reduced downtime, lower maintenance requirements and higher cleanliness provided by CHEMFILM® Flex Barriers lead to a significant increase in overall process yield and productivity.

Made from materials originally written by IEEE GlobalSpec.

This information is derived from, reviewed, and adapted from materials provided by Saint-Gobain Films and Fabrics.

For more information on this source, please visit Saint-Gobain FILMS & FABRICS.

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