Pressure switches or transmitters?

We have a large pumpstation we do work at, about 13 pumps feeding into a common manifold. Each pump has high and low Allen Bradley pressure switches, 26 total. They are fairly reliable, we probably replace or work on two/three a season. I think they run around $150-200 or so apiece.

They've decided to add 2 more pumps to the system which will now require rebuilding the electrical for the whole pump station as far as I know.

My question is, from a reliability and ease of maintenance/replacement standpoint, does it make more sense to replace all the pressure switches with a single pressure transmitter(for each pump) as well as add a plc and hmi? I was thinking the hmi would be nice for troubleshooting more than anything, just to make sure anyone working on it could verify they are actually getting a reading from each pumps transmitter.

Would this be a practical cost effective swap in the long term? Or am I going backwards? These pumps are all on motor starters, no VFD's, if it matters.

Thanks for the help.

My question is, from a reliability and ease of maintenance/replacement standpoint, does it make more sense to replace all the pressure switches with a single pressure transmitter(for each pump) as well as add a plc and hmi? I was thinking the hmi would be nice for troubleshooting more than anything, just to make sure anyone working on it could verify they are actually getting a reading from each pumps transmitter.

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I would use pressure transmitters for each pump and don't require any maintenance. We use these where I work at on the HVAC systems for the building that we need to maintian.

A big question for you is. What is this pumping station for? Why, I ask this is, knowing the app is important to give you a better answer.

Would this be a practical cost effective swap in the long term?

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Yes

Or am I going backwards?

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No

These pumps are all on motor starters, no VFD's, if it matters.

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It don't matter at, because it sounds like your system is constant pressure and the advanage when are starting loss head pressure or dead heading a pump.

Perhaps re-purpose a few of those pressure switches as High-High and Low-low's as backups to the pressure transmitters.
Why do you need one on each pump instead of just one on the header? Tell us more about your application and we can help more!

In general I expect a simple pressure switch to be more reliable than a transmitter. Are your switches rated NEMA 4X?

Even if you install the transmitters I'd keep the switches as backup. Compared to the cost of burning up a pump or trashing the seals a couple hundred bucks isn't much.

However, you can still add the transmitters. This will allow you to do additional diagnostics and trend. For example, if the pressure suddenly jumps you probably have a valve closed. If the pressure at a given flow increases over a period of months it may be time to pig your pipes. Etc. You can get pressure transmitters for a few hundred bucks now, so they are a small investment compared to potential equipment and energy savings the extra data can provide.

Transmitter are getting cheaper(cost wise) all the time. If you get some you can do WAY more with the data coming in than with a simple Hi-Normal-Lo pressure set up. Get one cheap enough it will do the job of both switches and allow you to trouble shoot longer term problems by looking at the trends in pressure much like Tom said. Cost will mainly be in the PLC/HMI set up as you may not have had one before but even then you can get some that are reasonalble in cost also!

Plcwill said:

A big question for you is. What is this pumping station for? Why, I ask this is, knowing the app is important to give you a better answer.

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All the pumps pull from a canal and discharge into a common mainline feeding irrigation circles-pivots.

mhulbert said:

Why do you need one on each pump instead of just one on the header? Tell us more about your application and we can help more!

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That, I'm not completely sure of. They start/stop pumps one a time manually to meet their needs. I've looked for a check valve after the discharge of the pump but all I see is an open/close valve, so I'm not real sure why they need individual. Unless the intake has one? I do know they need to operate a vacuum pump to prime each pump before they can fire it off.

Tom Jenkins said:

In general I expect a simple pressure switch to be more reliable than a transmitter. Are your switches rated NEMA 4X?

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I believe they are 4X, they are in a nice gasketed enclosure, industrial type. One of the problems we have is the vibration works the connections loose, rattles flex connectors loose, then eventually shorts wires out. I thought a simple pressure switch with an m12 connector would make for simpler-easier to replace solution. Even the customer could do it, if he needed too. Rather than call us.

Thanks for the help so far, I appreciate it.

Can you mount them differently and use a tube/braided hose to connect to the discharge header to avoid the ill effects of the vibration?

You can now buy transmitter/switches with integral displays.



Get one with two switch points and you won't have to add analog inputs to the PLC, or get one with an analog output.

The way you can mount these pressure switches or pressure transmitters is using 1/2" flexible conduit or low voltage cable that is coming junction box mounted on a non vibrating surface. This prevents any problems with the connections at the pump itself.

Using pressure transmitter with displays have one good advantage were you able to see the pressures at the pumps and saves you time, if you have bad pressure gauge at the pump.

They're some PLCs that have built-in HIMs like one fromUnitronics, which will work perfect for what you talking about.

Cow said:

I thought a simple pressure switch with an m12 connector would make for simpler-easier to replace solution.

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I meant to say pressure transmitter.

shawn_75 said:

Can you mount them differently and use a tube/braided hose to connect to the discharge header to avoid the ill effects of the vibration?

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That may be an option. Just the way the 1/4" pipe is put together right now looks like a jungle gym, with the pressure switches sitting on top of that, I think they vibrate a bit more than if they were actually screwed directly into the discharge piping. That was one reason I thought one single pressure transmitter would eliminate almost all of that.

Alaric said:

You can now buy transmitter/switches with integral displays.



Get one with two switch points and you won't have to add analog inputs to the PLC, or get one with an analog output.

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That's cool. I'll google and see who makes them and what they cost.

Plcwill said:

The way you can mount these pressure switches or pressure transmitters is using 1/2" flexible conduit or low voltage cable that is coming junction box mounted on a non vibrating surface. This prevents any problems with the connections at the pump itself.

Using pressure transmitter with displays have one good advantage were you able to see the pressures at the pumps and saves you time, if you have bad pressure gauge at the pump.

They're some PLCs that have built-in HIMs like one fromUnitronics, which will work perfect for what you talking about.

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I'll look into that too. I was leaning towards AD because it looked like a good platform for a beginner to start on. Good tech support, inexpensive software, etc but ultimately it'll be up to my boss to yaay/naay my idea. I just want to have my ducks in a row before approaching him and figured there might be a better way than the pressure switches we've been having trouble with.

Heck, he might just be happy with mounting them on a seperate stand and running hose to them to help eliminate the vibration.

Thanks again guys for all the input.

If you click the picture it will link you to the manufacturer.