Article 56: Pump Repairs – a Fuel to the Economy
After Bob’s visit last month (P&S, June 2015), Jim (plant maintenance manager) decided to speak with his boss about the issue with the pump efficiency Bob discovered using Bob’s company PREMS-2A unit (www.pumpingmachinery.com/pump_school/pump_school.htm, PVA module #10). Charlie came to the Blue Creek water plant about a year ago and had not yet been keenly aware of all plant’s history and details about these pumps.
- What you got, Jim? Make it quick, I have a corporate meeting to head to after lunch. They want to talk about influent screens problems at the Poopers Willow wastewater processing plant, and asked all watershed plant managers to attend. I run a clean water plant and not sure why they need me at that meeting, but if the bosses call I’ll be there.
- Ok, boss, just wanted to let you know, this guy from the Duck Pump company did some energy efficiency testing of our main water booster pumps here and found they need some fixing. He says their efficiency low.
- Really? I had a similar issue with energy back at my days running the Clowns-for-Rent company. We had a ton of old light bulbs installed all over the facility, and this guy came and did some efficiency testing and suggested we switched to some sort of energy efficient light fixtures. Tons of money involved, but apparently we still saved some money overall. How much savings you are talking about?
- Well, he figured we burn nearly $125K extra in wasted energy, and in just one repair it will get things up to snuff, and we recoup the cost in just about a year.
- Hmmm… So it is about $125K repair job? Still, a lot of money. I do not think we got it in this year budget.
- That’s what I told him too. Anyway, Charlie, just wanted you to know.
- Thanks. Let’s talk more on this tomorrow.
The next day Jim and Charlie got together to look over a fresh quote on the pump repair-and-upgrade which Bob emailed to Jim. If was $143.6K, somewhat over the budgetary estimate he gave him earlier verbally, but the extra money was justified by switching from a single to double mechanical seal, which Bob recommended as a good thing, to save water, and improve reliability of the unit.
- So how long will it take them to do the upgrade, Jim? - Charlie was examining the numbers, - it says eight to ten weeks, that long?
- Yeah, - that’s not bad. The last time they did it took them about the same. They do pretty good job. We did the last pump about four years ago, and that is usually how they take care of us.
- Every four years a pump? Isn’t that a bit too often? Granted I did not have a chance to learn about our pumps yet, but when I worked at Clowns-for-Rent, we had several big blowers in the back yard, to blow out clowns uniforms after they come back from a day of clowning, and these blowers seem to had lasted forever. I was there of about twenty years and do not remember if we ever had any issue with these. The Master Clown was very pleased with our predictive maintenance program there.
- That’s right. That is exactly what Bob is saying. Duck Pumps gives us a full one year warranty, and if the pump stays idle most of the time, they extend a warranty for two years. This way, the less we run the pumps, the more money we save, Charlie!
- You know, Bob, - let’s go to the store room, I want to see one of these pumps, do you have a spare there?
- I sure do. Actually I have two spare units, and four installed ones. We usually only run one pump at a time, but during peak hours we fire up the second pump, to get more water to folks if the Bubble Noodle plant is down and we need to cover for them.
In the shop, Charlie and Bob, joined by the mechanic Rusty, saw the pump. Store manager, Grady Cricket, put a newspaper aside and got up to meet them:
- This is the pump, Bob? Does not look like a $100K+ job to me!
- Well, I meant we have a couple of spare rotors, not a complete pump. Usually, when they do repair, they keep casing in place, just pop the top of (this is what makes it a split case pump), and just remove the shaft with the impeller and bearings with their housing.
- OK, I see. So, in his quote, Bob mentioned changing wear rings to restore clearance. How big are those clearance originally, and how much do they open up by wear?
- It is all in the pump manual, Charlie. I do not remember the exact number, because the manuals are at the engineering department downtown, and I do not get their often. But I think these are roughly 0.020” or so, and get bigger as they wear.
- But how do they wear? – does impeller rings touch the casing ring? I am not an engineer, but would imagine the Duck Pump would design the shaft big and stiff enough so it does not deflect very much to touch.
- I would think so, agree. If they touch, something is wrong – either bad design, or bearings are gone. No, the main reason for wear is probably by the pumpage.
- Pumpage? But we pump clean drinking water! How abrasive it can be?
- Yeah, you are right. I don’t know either, pump it is a bit above my pay grade. We can ask Sandy Mixups in engineering. She is an engineer at the corporate, and I saw her a few times when she came to see the plant a couple of years ago. She would have all the manuals and data. Rusty, is this stainless?
- Let’s see, - Rusty picked a dial indicator base and popped the magnet over the shaft surface, - Does not stick – stainless!
- That’s right, - Jim’s eyes lit up, - No wonder, it is expensive. What about impeller? Hmmm... That too. The whole thing is stainless. How about the ring? No! – magnet is stuck to it! The wear ring is not stainless! What’s going on here? Is this why it is wearing out? Maybe it just rusts away (no pun intended, Rusty!). You know something – we better get Sandy to come to the plant, and may as well as setup a meeting with Bob to go over his quote.
- Sounds good, guys, - Charlie was pleased what he was learning at the storeroom (he wanted to get there one of these days anyway), although what he discovered was more questions than answers, but… - Let me know when you set up the meeting. Let’s do it sometime in July.
Next month, - meet Sandy, - and enjoy the discussion she will be having with Bob from the Duck Pump company. Will a non-magnetic ring Charlie and Jim discovered turn out to cause rusting and wear?
1. Nelik, L., “Pump Repair and Upgrade Standards”, pages 16-17, Pumps & System, May 2012
2. Kale R.D., and Sreedhar B.K., “A Theoretical Relationship Between NPSH and Erosion Rate for a centrifugal Pump”, ASME 1994, FED-Vol. 190, Cavitation and Gas-Liquid Flow in Fluid Machinery”
3. Nelik L., “How Much Energy is Wasted When Wear Rings are Worn to Double Their Initial Value?”, March 2007