Pump Control

If you ask the internet about duplex pumps (What are they? How do they work? Why would or should you use them?), you will get a variety of answers.

Some sound like they are talking about two pumps, usually with a shared source, that may or may not work together. Others sound more like two offset pumping mechanisms in one mechanical unit. That’s two very different concepts to be linked by one name.

So which is it? Are they interchangeable? Does it matter? Let’s take a look.

Pump control was once an exciting job that, done well, kept pumps running maintenance free for many years at a time. Now, you may be lucky to have a pump stay out of the repair shop for two years – some only for six months.

What happened to pump control? Why are so many needing repairs so frequently?

The truth is, the right way to do pump control has been forgotten by many. It happened as older engineers, technicians, and operators retired. It happened as fluid dynamics classes in college spent less time on pumps....

Among the most common methods for pump control in lift stations is the use of multiple cable suspended float switches. While this method may appear to be the least expensive, it also involves the most risk and hassle.

One of the biggest unforeseen costs with multiple individual floats is maintenance. Many lift station techs plan on replacing one float switch per year due to the lack of quality of these less expensive units. In addition, having several cable suspended float switches in the same well will often result in tangled floats.

Installing a variable frequency drive on a pump motor is all about energy efficiency and pump longevity. These are good goals to have, but that doesn’t mean that a VFD will give you the payback you’re looking for in every application.

How do you determine if you need a variable speed drive?

There are two main questions you must ask yourself:

1. Can I achieve a constant flow or pressure with a VFD?
2. If so, how will a VFD affect pump efficiency and performance?

Back up pump control is a critical part of any pump control application, ensuring that failure does not result in a potentially hazardous overflow or the unwanted emptying of a tank. Ideally, back up sensors work independently from the control system, so that failure of the primary controls will not disable them.

This means basic control features such as hysteresis...

Rapidly changing liquid levels can overwhelm a single pump, and cause excessive wear and tear. To prevent this, additional pumps can be added to control the liquid level.

A common example of this is a duplex lift station; liquid is pumped from a well to a higher elevation, where gravity can carry the liquid to the next station. Lift stations are used primarily in the wastewater industry, to carry liquid waste to the treatment plant.

A duplex lift station uses two pumps: a lead pump and a lag pump...

Last week, we covered a few trip points (six, to be exact) programmed into the IRU ultrasonic sensor series. Using either of the two with hysteresis is a good way to combat chatter – a phenomenon that happens when a single switch point flutters between open and close.

Chatter is usually due to relatively slight turbulence in a tank, when the level sits just above or below the switch point. It wreaks havoc on pumps because it turns the pump on and off in rapid succession, adding extreme wear and tear.

In addition to the various types of point level sensors for pumping stations, a more advanced approach is growing in popularity. Many businesses and municipalities are using continuous level sensors. Some popular sensors for continuous level measurement are submersible pressure transducers, ultrasonic and radar sensors, and level probes.

Switching to a continuous level sensors is a step toward...

In this post, we will cover duplex pump control for lift stations. In the weeks prior, we gave a good overview of lift stations, and covered simplex pump control. Check out those posts for more detail.

Duplex Lift Stations

Duplex lift stations have two pumps:

Sensors play a key role in pump control for Lift stations. Without good working sensors, lift stations can overflow, pumps can be ruined, and power can be wasted. Over the next few weeks we will be providing a series of posts that cover the various types of sensors that can be used for duplex and simplex pump control, override sensors to provide back-up pump control, and some of the benefits of continuous level measurement vs. point level sensing.