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Pump Overhauls & AHU Overhauls


Seasonal Overhauls for Chillers: Chapter 4


Pump Overhauls


We've discussed the necessary steps to maintain the main components of a chiller. If you've followed them, it's time for water circulating equipment. This module will help you understand how to overhaul pumps. Skip to quiz!


Pumps


Recall that a chiller system generates cold water. Do you recall how do we circulate the cold water? Water pumps are used to circulate this cold water throughout the building.


Two sets of pumps are used for cold water pumping:

  • Primary pumps, and

  • Secondary pumps

The primary pumps return water from a building to the chiller, and secondary pumps supply cold water from the chiller to a building. Both these pumps are of centrifugal type.


We should perform maintenance and repairs on system components like pumps and valves during a shutdown. The goal is to identify deficiencies that can be addressed during the shutdown period. This ensures that the machine will be ready to start as soon as required.


We need to follow the below steps to ensure a problem-free restart of the pump:

  • Check that the pump spins freely,

  • Checking vibration,

  • Check coupling condition,

  • Lubricate components,

  • Valves in a correct position for start-up, and

  • Inspect pump base

Let’s discuss each of them in detail.


The most important thing to check on centrifugal pumps is that the pump still spins freely. It's possible the pump could contain solidified products or have mechanical issues after sitting idle for months. Lockout the pump, remove the coupling guard and turn the shaft to check this.


When turning the pump shaft, listen for rubbing sounds. Most centrifugal pumps should turn by hand. If the pump doesn’t turn, don’t force it. Instead, take it apart and inspect it.


Since we have removed the coupling guard for checking the rotation of the pump, now is an excellent time to check the condition of the coupling. Look for evidence of wear. This could include rubber dust or plastic chunks under the coupling. This is evidence of misalignment; the pump should be re-aligned before restarting.


Recall that you laid up the cooling tower with chemicals before shutdown. If chemical residues remain inside feed pumps and feed lines, it can cause many problems.


For example, these crystals can settle over the pump impeller and increase vibration and noise. If the crystals are left behind, they can even travel through the feed lines and prevent check valves from seating properly. To avoid these issues, make sure you have flushed all your chemical pumps with water.


The other reasons for pump vibration are:

  • Damaged impeller,

  • Misalignment of shafts,

  • Water leakages, and

  • Weak foundation.


The misalignment of shafts is one of the vital vibration sources in centrifugal pumps. To avoid vibration problems, we have to check the alignment of the pump with the motor during overhauling.


We can check the alignment using a dial indicator. We can also use an advanced instrument like a laser shaft alignment tool for precise measurement.


Next, we must lubricate the pump bearings during the overhaul. It is similar to greasing your compressor bearings. Do you recall how do we lubricate bearings? We use a grease gun to fill grease inside the bearing.


To apply grease on the pump bearing, connect the flexible hose to the nipple on the bearing. Start pressing the lever until grease fill inside the bearing.


Remember how we checked the strainer of a cooling tower feed pump? The strainer of the primary pump is checked in the same way. If the strainer is clogged, we need to clean it.


First, turn off the water pump and close the inlet and outlet valves to clean the strainer. We remove the nuts of the strainer to remove the strainer cap. We then remove the mesh from the strainer and clean it with water. Finally, we have to reassemble the strainer.


Air may enter into the pipe during a shutdown, and you would have to prime the pump to remove the air. Sometimes, pumps used in a chiller system are self-priming type. This device can discharge water while also getting rid of the air by creating a partial vacuum.


If the pump is not self-priming, we need to manually prime it.


We need to open the suction and vent valves. Opening these valves allows liquid to fill the pump and air to escape. Ensure the discharge valve is open so that water flows throughout the building.


Now that the pump is operating do a final check of the base to ensure that mounting bolts are tight. Inspect the pump base with a spirit level to ensure that it is flat leveled out.


Next, we need to check all the valves on the feed line. We should ensure that valves are in the correct position. We also need to ensure that the wheel on the valve is not seized up, and we can turn it smoothly.



We need to follow the below steps to ensure a problem-free restart of the pump:

  • Check that the pump spins freely,

  • Check coupling condition,

  • Lubricate components,

  • Valves in a correct position for start-up, and

  • Inspect pump base


 

AHU Overhauls


Have you ever thought of how the seasonal shutdown can affect the air handling unit? This module will allow you to learn about air handling unit problems. Going through this module will prepare you to avoid these problems next seasonal shutdown. Skip to quiz!


AHU


It's 6:30 A.M on a sunny Monday morning in January. You enter the office's main lobby and realize you are standing in a puddle of water. You noticed that the ceiling tile is soaked and on the verge of collapse. Welcome to Monday morning.


Recall that ceiling suspended AHUs are hung from the ceiling. That's what ruined your Monday morning! You have no choice but to fix them because they keep you warm during cold winter days.


As the temperature gets colder and we head into winter, we always talk about things like bundling up and getting your snow shovel ready. But one thing we often forget about is overhauling AHUs. This can lead to such bizarre Monday mornings.


During overhauling, we inspect all the main components of an AHU. Do you recall the main components? AHU contains:

  • An air filter,

  • Blower,

  • Heating and cooling components.


Overhauling AHUs is similar to what you have done for routine maintenance. Do you recall AHU's routine maintenance procedure? During routine maintenance, we check filters, blower, belt and pulley drive, bearings, and coils.


Some believe overhauling main components just like routine maintenance is enough for seasonal overhaul. Think again. Just like your cooling tower, water in AHU coils can also freeze if it gets exposed to cold air.


Do you think closing the dampers will prevent freezing of the coils? No! Closing dampers cannot completely ensure no air entering inside an AHU.


You probably might have noticed that air leaks in from the bottom of the door even if it's locked in place. In the same way, the building stack effect can also cause cold air to enter through closed outdoor air dampers.


To avoid frozen coils this winter, you should drain them during overhauling. After draining, we should flush the coils with a water mixture. Make sure you also clean the exterior of the coil.


After cleaning, we should ensure that no water particles are left on the coil. We need to blow compressed air through them to ensure no liquid is present.


Next, fill the coil with a mixture of propylene glycol and water. We need to ensure that this mixture has a freeze point lower than the coldest outdoor temperature. Be sure to use inhibited glycol and check for proper concentration or freeze point percentage.


Next, we need to clean condensate pans. Make sure the condensate pan drain opening is completely clear of any dirt or debris. This will ensure that condensate can drain freely.


It is important to note that if an antifreeze sensor is ON, it will trip at a set point. If our system is OFF and cold outside air enters the coil, it can create unnecessary alarms. We need to switch OFF the freeze sensor if our system is not operating to prevent nuisance alarms.


If our system is not drained completely, we need to check whether freeze stat controls are operational. We also need to install freeze alarms, if not present.


Lockout Tagout is a procedure used to ensure that equipment is shut down and tagged. This procedure is followed before overhauling any component of the chiller. It is used to prevent people from accidentally turning ON the chiller while overhauling.



We have to drain, and clean coils pump glycol into the coil during overhauling. We need to make sure the condensate pan drain opening is completely clear of dirt or debris. Apart from these components, we overhaul the main components of AHU similar to routine maintenance procedures.


 

Question #1: Which pump type is most commonly used in chillers to supply cold water from the chiller to a building?

  1. Centrifugal

  2. Rotary

  3. Reciprocating

  4. Vane

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Answer: Centrifugal

The secondary pumps supply cold water from the chiller to a building.

These pumps are of centrifugal type.


Question #2: What parameters need to be checked when overhauling pumps? (Select all that apply)

  1. Checking vibration

  2. Check coupling condition

  3. Check mechanical seal

  4. Check pump head

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Answer: Checking vibration

Check coupling condition

Check mechanical seal

Following steps are taken during pump overhauling:

  • Check that the pump spins freely

  • Checking vibration

  • Check coupling condition

  • Check mechanical seal, and

  • Check oil and lubrication levels


Question #3: Which of the following tools can be used to measure pump misalignment? (Select all that apply)

  1. Pump head

  2. Dial indicator

  3. Multimeter

  4. Laser shaft alignment tool

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Answer: Dial indicator

Laser shaft alignment tool

Following steps are taken during pump overhauling:

  • Check that the pump spins freely

  • Checking vibration

  • Check coupling condition

  • Check mechanical seal, and

  • Check oil and lubrication levels


Question #4: What is the correct sequence to clean the strainer?

  1. Remove the mesh from the strainer

  2. Inlet and outlet valves of the strainer should be in closed condition

  3. Water pump should be switched off


Scroll down for the answer...


















Answer: Water pump should be switched off

Inlet and outlet valves of the strainer should be in closed condition

Remove the mesh from the strainer

First, turn off the water pump and close the inlet and outlet valves to clean the strainer.

We then remove the mesh from the strainer and clean it with water.


Question #5: The overhaul for the main components of an AHU is the same as routine maintenance.

  1. False

  2. True

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Answer: True

True. We follow the same procedure as routine maintenance for overhauling an AHU.


Question #6: What is the correct sequence for prepping the AHU cooling coils for the winter?

  1. Purge coils with compressed air

  2. Drain the coils

  3. Add glycol to the coils

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Answer: Drain the coils

Purge coils with compressed air

Add glycol to the coils.

The correct sequence for winterizing an AHU cooling coil is Drain the coils, Purge coils with compressed air, Add glycol to the coils.


Question #7: Which of the following maintenance procedure needs to be done during AHU overhauling? (select all that apply)

  1. Preparing report

  2. Heating coils

  3. Switching OFF freeze sensor if the coil is drained completely

  4. Draining coils

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Answer: Switching OFF freeze sensor if the coil is drained completely

Draining coils

We drain the coils and switch off the freeze sensor if AHU is not operational during winter shut down.


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