In our latest case study, we’re going to talk about a recent enquiry we received to supply two air-driven high pressure filter press feed pumps to a UK filter press manufacturer.
So, what is a filter press?
The first filter presses came into operation in Britain in the 1850’s and were used to separate seed oils. But it took another 100 years for the technology to fully develop and become a viable and cost-effective choice for a variety of industries and applications.
A filter press is a machine which works to separate solids suspended within a liquid known as a slurry. A filter press turns the slurry into water and dry filter cake.
They operate by receiving the slurry from a filter press feed pump which compresses the mixture. It separates out the variable quantities of solid-laden slurry from the water carrying it.
Filter presses and the pumps supplying them can bring big benefits to a company’s business operations:
- Removing water from slurries and sludges to cut wastewater treatment costs
- Reducing transportation and disposal costs
- Maximising plant effectiveness
- Enabling water to be reused to maximise process efficiency
How is a filter press used?
When fed by a special filter press feed pump, a filter press can be used for:
- Polishing
This removes impurities from liquids such as small clumps of sediment, water and microbes. This is often carried out with fuel.
- Fixed volume or batch
The filter press can hold a large quantity of solids, so it can be stopped and started to remove the solid waste which has been separated. This is called cake, sludge or filter cake.
- Variable volume
These units have a diaphragm or membrane plate which separates the cake more effectively than other methods. They can produce dry content of between 30% and 80% and reduce filtration time by up to 50%.
The pumps used to supply filter presses are usually positive displacement pumps as these can handle the increasing back-pressure as the filter press becomes filled with material. Filter press pumps can be designed with automatic start and stop between batches, and also to allow the filter press to be cleaned when required.
Where are they used?
One sector that has widely adopted the filter press as a key part of its production process is the water and wastewater industry. It’s ideal for this sector because these processes generate large amounts of slurry.
Indeed, the filter press has been a great addition to these industries as it’s the most effective way to separate solids and liquids during the dewatering process. The filter press can also be placed some way from the slurry tank, and is fed by filter press pumps connected by suction and discharge piping.
How do they work?
As the slurry is pumped into the filter press, two chambers are filled with the material. As the chambers fill, compressed air is shifted from one chamber to the other by a linked shaft that enables the chambers to move simultaneously. This back-and-forth movement forces liquid out of one chamber and into the discharge piping. At the same time, the other chamber is being filled with liquid.
When the chambers reach capacity, the liquid is filtered out by the compressed air, leaving behind solid slurry, sludge or filter cake ready to be disposed of.
Perhaps the biggest advantage of this process is that instead of having to get rid of massive amounts of wet slurry, the operator is left with water and smalls amount of filter cake. This brings down disposal costs considerably.
Therefore, a key component of the whole process is the filter press feed pump which sends the solid-laden fluid to the filter press.
Introducing the Air Operated Double Diaphragm pump
An Air Operated Double Diaphragm (AODD) pump is driven by air and as mentioned, has two separate diaphragms which work individually to separate the water and particles. These fill with fluid before being discharged through an outlet manifold.
As mentioned, AODD pumps are a type of positive displacement pump that uses standard compressed air for power. They have impressive suction lift properties and can handle sludges or slurries with quite high amounts of grit and solid particles.
These pumps are used at production facilities of all sizes, in a variety of different industries for a range of applications including highly viscous liquids. In short, from petrochemicals and precious metal mining to food and beverages, these air-driven filter press pumps are proven, highly popular and reliable.
High pressure AODD pump
Diaphragm pumps are also available in high pressure designs. In fact, these special high-pressure air-driven filter press pumps models work in just the same way as standard AODD pumps.
The big difference is that the high pressure design has a built-in internal pressure amplifier with external piping. These enable the units to deliver pressures of up to 16 bar which is essential for many filter-press applications. They are also widely known as 2:1 pumps.
In addition, many designs feature high-density polyethylene construction. This is seven times more resistant to abrasion than polypropylene and more hardwearing than steel, iron and aluminium. This makes these pumps perfectly suitable for use with the wide range of chemical formulations found in many wastewater and water treatment regimes.
What’s more, air-operated diaphragm pumps have a number of built-in advantages for filter-press feeding – they have run-dry capability, are easy to control and have a gasket-less mechanical design. Plus, there are no rotating parts, rotary shaft seals or drives.
Our specification for the client
Here at North Ridge Pumps, we can supply a wide range of pumps for a variety of filter press feed applications.
What’s more, we’re not limited to just one pump technology. Our unrivalled expertise enables us to offer a tailor-made solution, not something off the shelf. So we always choose the most cost-effective pump for any specific client, project and application.
For this project brief, we opted for the high pressure AODD filter press feed pumps to be manufactured in AISI 316 Stainless Steel – a chemical resistant hard wearing material often used for abrasive material.
Normally, diaphragm pumps can generate pressure up to 8 bar, but for this application, we constructed two 1.5” high pressure diaphragm pumps which could handle slurry at up to 16 bar.
We made the pumps out of hardwearing AISI316 stainless steel, with Santoprene™ internal parts ensuring maximum suitability for this filter press feed application.
Santoprene™ is a high-performance thermoplastic vulcanisate which combines the properties of vulcanised rubber with the processing simplicity of thermoplastics.
In fact, Santoprene™ is a durable and functional sealing solution specially designed for a variety of applications. It’s been adopted across a broad range of market segments including industrial, construction, automotive, household, electrical and healthcare.
We manufactured the two air-driven filter press pumps to handle flows up to 200L/min, solids up to 6mm diameter, and we delivered them to the client in 4 to 5 weeks as promised. In addition, the pumps were designed to meet ATEX regulations.
If you have a dewatering application needing the transfer of fluids, solids or viscous liquids, and aren’t sure which pump to specify, speak to North Ridge Pumps on 01773 302 660 or visit www.northridgepumps.com to see how we can help.
