Spoilt for choice – the rights and wrongs of pump selection

Pumps are used by manufacturers in a multitude of industries for a huge variety of liquid-transfer tasks.

There is a massive and complex range of pumps available, and getting the right one for your process, material and conditions can be an intricate decision.

For instance, do you need a centrifugal or a positive displacement model? One with pistons or gears? Should you consider packing or mag drive? Will plastic suffice or do you need stainless steel? How big should it be and how should it be set up? How much are you looking to pay and how often are you willing to repair or replace it?

Then, when it comes to hazardous and hostile liquids, the choice becomes not just difficult but critical.

If a pump fails you could have an explosion and people could be maimed or killed

Tony Keville, managing director, Tomlinson Hall

“If you get pump selection wrong it can be a disaster,” says Steve Schofield, chief executive of the British Pump Manufacturers’ Association (BPMA).

And he doesn’t mean this in the metaphorical business sense of the term. “It can kill people,” Schofield warns.

Tony Keville, managing director at pump distribution firm Tomlinson Hall, confirms Schofield’s warning about getting it wrong in this field.

“If a pump fails you could have an explosion and people could be maimed or killed,” he says. “If a seal leaks you could have a cloud of explosive material – a spark would then be very dangerous.”

Hostile liquids are active in the processes of several sectors, Keville says.

“In the chemicals industry you might have corrosive materials being pumped. In the nuclear sector you could have radioactive materials. In the water industry there may be treatment chemicals, while in pharmaceutical and food production there can be biohazards.”

Handle with care

The first job when specifying a pump for hostile product is to know exactly what you’re handling. But often manufacturers are not as are not as clear as they would be, warns David Brown, managing director of pump maker Borger UK. “Sometimes clients don’t know what they are dealing with,” he says.

“For example, in the waste industry they might not know the chemical make-up of the product they are pumping. But this is key.”

Even if they avoid the worst case scenario, companies will be hit hard in the pocket for bad pump selection.

“Often an incorrectly specified pump will keep working but will start to cost a fortune in maintenance and spare parts,” says Brown.

“You will get ongoing problems. It is far better to get it right first time.”

Schofield says pump manufacturers will occasionally question the specification given to them by a client, and sometimes carry out their own tests.

“The hazardous product sector is fairly niche but many of our members specialise in it,” he says.

Often an incorrectly specified pump will keep working but will start to cost a fortune in maintenance and spare parts

David Brown, managing director, Borger UK

“Small changes in temperature or use of abrasives can have a massive effect on pumps. When I worked in this sector I could tell when someone had started using abrasives by the corrosion on the pump.

“Pump manufacturers generally don’t question the expertise of the client, but sometimes, with all your experience, something jumps out at you. You ask them why they are using a certain material at a certain temperature.”

There is a need for clear communication between the client and manufacturer. Sometimes companies have their own reasons for selecting a certain pump.

“One of our members makes pumps for liquid sulphur. This is really nasty stuff and you have to get it just right,” says Schofield.

“I went to see one client that was making washing powder for clothes and it had a zirconium pump that was being used for sulphuric acid and wearing out every three months. I advised them to change the pump, but the customer said they would rather keep replacing this very expensive equipment than change its process, as it had a formula that worked and produced the right product for its own customers.”

Elsewhere, a seemingly harmless product may in fact need to be treated very carefully.

“In the nuclear industry, you might have a pump dealing only with water – but water that has been through a nuclear process so has to be contained,” says Schofield.

“You might need a mechanically-sealed pump where there is no way the liquid can escape to atmosphere.”

In the know

So the more information a customer can give a pump maker the better chance of getting the right solution.

However, Brown says you have to use your instinct a bit sometimes.

“Getting to site and taking measurements is useful, even supplying trial pumps.”

Keville says pump specifiers need to understand fine details of the liquids they are handling. Different strengths of the same acid can require pumps made from totally different materials because of the varying reactions that can occur, he says.

After liquid make-up, Keville says the process the pump is being used for is the next thing to consider.

The many factors to understand here include flow rate, concentrations, specific gravity, viscosity, temperature, and presence of solids.

Once materials have been chosen for a pump, manufacturers have to decide which type they require.

Schofield says: “There are two main families of pump – centrifugal and positive displacement.

“The former uses an impeller driven by a motor to put kinetic energy into a liquid; the latter is like passing something hand to hand. The more viscous the product you’re handling, the more likely you are to use a positive displacement pump.”

The Process Industry Forum explains that centrifugal pumps have no drive seals, so run very little risk of fluid escape. This is clearly a plus for handling hazardous materials.

One of our members makes pumps for liquid sulphur. This is really nasty stuff and you have to get it just right

Steve Schofield, chief executive, BPMA

However, positive displacement pumps can produce a near-constant flow of liquid and are often selected when dealing with suspended or fragile solids. So it is a decision to be made on a case-by-case basis.

Once that decision has been made, each family of pumps then breaks down into a multitude of sub families such as rotary style pumps (including those using gears); reciprocating, including piston-driven; linear type; and diaphragm.

Centrifugal pumps, meanwhile, can include mechanically actuated, hydraulically actuated, solenoid and air-operated double diaphragm. Each type has its own features and benefits.

There are also different ways of ensuring liquids can’t escape from centrifugal pumps – you can use traditional packing methods, mechanical seals or mag drive versions that use magnet technology.

Kitted up

And on top of all the above decisions, pump users have to make sure their kit complies with industry regulations.

“If you want to operate on a petrochemical plant you have to meet API specifications,” says Schofield.

“Pumps for sprinklers in hotels have to meet different standards, while there are other criteria for food production. That’s why you get industry-specific pumps, and many of our members stick to one sector.”

Schofield says it is “highly unlikely” anyone will create a one-size-fits-all pump for different sectors and applications due to the different factors discussed.

Pumps for sprinklers in hotels have to meet different standards, while there are other criteria for food production. That’s why you get industry-specific pumps

“You also don’t get many bespoke pumps because of the sheer cost of starting from scratch,” he adds.