How Do You Choose Between Two Big Vacuum Pump Brands?

Walk into any plant that runs vacuum and you'll hear strong opinions. Some engineers swear by one brand for life. Others switch depending on who gave the best quote that quarter. Two names that come up constantly are nash liquid ring vacuum pumps and elmo rietschle vacuum pumps, and for good reason, both have been around a long time and both turn up in all sorts of industries. But here's the thing nobody says out loud. The brand on the nameplate matters less than whether the pump, the seal water system and the cooling all suit your duty. At Courtney & Nye we don't sell pumps, we work on the cooling and heat exchanger side, so we see what happens when the pump choice and the rest of the system don't line up. This post is about avoiding that.

Start With the Process, Not the Brand

Before you even look at a catalogue, write down what the vacuum has to do. What gas or vapour are you pulling? How wet is it? Does it carry solids, fibres or condensables? What vacuum level do you need, and what flow rate at that level? Is the duty continuous or on and off? What's the inlet temperature and what's downstream? Those answers shape everything. A pump that's perfect for a clean, dry duty might struggle with wet, dirty gas, and the other way round. People often start by saying we've always used this brand, so let's buy another one. Fair enough, familiarity has value. But it's a poor substitute for checking the pump curve against your real conditions.

How Liquid Ring Pumps Work, Briefly

Quick refresher for anyone who hasn't opened one up. A liquid ring pump has an impeller mounted off centre inside a casing partly filled with liquid, normally water. When the impeller spins, the liquid is thrown outward into a ring against the casing wall. Because the impeller is off centre, the spaces between the blades grow and shrink as they turn, which draws gas in and then compresses it. The liquid acts as both seal and piston. There's almost no metal to metal contact in the compression zone, so wear is low, and the pump handles wet gas and small amounts of liquid carryover that would damage many other designs. The trade off is that it needs a steady supply of seal liquid, and that liquid has to be kept at a sensible temperature.

Where liquid ring pumps Make the Most Sense

These pumps shine in tough, wet, messy duties. Paper machines, chemical processing, distillation, filtration, degassing, drying, priming systems and many other applications use them because they tolerate saturated gas and vapours that would foul dry running pumps. Compression is close to isothermal, since the seal liquid soaks up heat, which helps with gases sensitive to temperature. Efficiency isn't the headline, and the ultimate vacuum is limited by the vapour pressure of the seal liquid, but for reliability in rough conditions it's hard to beat. Plenty of nash liquid ring vacuum pumps have run for decades in plants that never gave them much love. That reputation is earned, though it assumes someone looked after the seal water side.

Where Other Technologies Fit Better

Now let's be fair to the other side of the debate. Dry running designs such as rotary vane, claw and side channel machines have their own strengths. The elmo rietschle vacuum pumps range, as far as we know, covers several technologies beyond liquid ring, so check the current catalogue to see what's offered for your duty. Dry pumps can reach deeper vacuum and use no seal liquid, which means no wastewater and no contamination of the liquid, though they may be less happy with wet gas, particulates or aggressive vapours. Efficiency can be higher too. So the real question isn't which brand is better. It's which technology suits the duty. Sometimes that's liquid ring, sometimes it isn't, and a good supplier will tell you honestly which one you need.

Comparing Brands the Sensible Way

When you're comparing nash liquid ring vacuum pumps with elmo rietschle vacuum pumps or any other makes, make the comparison fair. Give each supplier the same duty sheet. Ask for performance curves at your operating conditions, including seal water temperature, because published curves are often based on a standard temperature that may not match your plant. Compare power consumption at your duty point, not at maximum. Check materials for casing, impeller, shaft and seals against your gas and seal liquid chemistry. Look at weight, footprint and connection sizes. Ask about service intervals, spare parts availability and local support. A slightly cheaper pump with poor local service can cost far more over time. Always check the current specs from the manufacturer, not an old brochure.

The Seal Water Side Everybody Underestimates

Here's where Courtney & Nye comes in. Whichever brand you pick, the pump turns motor energy into heat, and most of that heat lands in the seal water. As the water warms, its vapour pressure climbs, the vacuum you can pull drops, and long term you risk cavitation damage. So you either run once through with fresh water, which is simple but thirsty, or recirculate it through a cooler. That cooler could be a plate unit, a shell and tube unit or an air cooled arrangement, and the right choice depends on how clean the seal water is and what cooling source you have. Undersize it and you quietly lose vacuum capacity every summer. Choose the wrong materials and you'll be replacing it in two years. It's not a side issue, it's half the system.

Installation and Maintenance Basics

A good pump installed badly still disappoints. Make sure the seal water supply is steady and at the right flow, and that the piping doesn't create air pockets. Fit a strainer or filter ahead of any cooler so debris doesn't clog the passages. Support the pipework so the pump flanges aren't taking strain. Provide instruments for temperature, pressure and vacuum, because trends tell you things long before alarms do. Maintenance is refreshingly simple. Watch seal water temperature, motor current and vacuum level, check bearings and mechanical seals on schedule, and look out for scale buildup inside the casing in hard water areas. Keep a log. Old readings make troubleshooting quick when performance slips, and performance always slips eventually.

Common Mistakes When Buying Vacuum Equipment

The same slip ups keep happening. Choosing by brand loyalty without checking curves. Ignoring seal water temperature in the performance data. Underestimating how much cooling is needed on the hottest day. Forgetting about contaminants that will end up in the seal water. Buying the pump and the cooler from different sources and never checking they work together. Skipping filtration. Oversizing the pump, which wastes power and can make control awkward. And treating the cooler as a commodity, when a mismatched one quietly cuts capacity for years. Ask awkward questions before you buy, not after. If a supplier gets defensive when you ask for calculations, that tells you something useful about how they'll behave when something goes wrong.

Conclusion

So how do you choose between the big names? Start with your process, check the performance curves at your real conditions, compare total cost over the life of the equipment and look closely at service and support. Both nash liquid ring vacuum pumps and elmo rietschle vacuum pumps have solid reputations, but reputation doesn't replace a proper duty check. And don't forget the seal water system, because a well chosen pump with a weak cooler will never give you the vacuum on the datasheet. If you need help sizing or choosing the cooling side, or want a second opinion on a spec before you commit, Courtney & Nye is happy to take a look and tell you plainly what we'd do.

FAQs

What are nash liquid ring vacuum pumps used for?

They're used for pulling vacuum in wet or dirty duties such as paper making, chemical processing, distillation, filtration, degassing and drying. The liquid ring design tolerates saturated gas and small amounts of liquid.

Are elmo rietschle vacuum pumps all liquid ring?

No, as far as we know the range covers several technologies, so check the manufacturer's current catalogue for what's available for your duty.

Which is better, nash liquid ring vacuum pumps or elmo rietschle vacuum pumps?

Neither is better in general. The right pump depends on your gas, vacuum level, flow rate, contamination and running hours, so compare performance curves at your real conditions.

Why do liquid ring vacuum pumps need cooling?

The motor energy turns into heat in the seal water. Warmer water has a higher vapour pressure, which limits vacuum and can cause cavitation.

How do I cool the seal water on a liquid ring pump?

Either use fresh water once through, or recirculate it through a cooler such as a plate, shell and tube or air cooled unit, with a small make-up stream.

How long do liquid ring vacuum pumps last?

Often many years, even decades, with clean seal water and regular maintenance. Corrosion, scaling and neglected bearings or seals shorten that.

How do I compare vacuum pump quotes properly?

Give each supplier the same duty sheet, ask for curves at your seal water temperature, compare power at your duty point and check service support.