There’s a wide variety of scenarios that may require a service technician, facility manager, or manufacturer’s rep to troubleshoot a pump. Regardless of the circumstances, using a methodical approach is best when diagnosing a pumping problem.
Taco Comfort Solutions discovered that 80%-90% of the calls the company receives about commercial pump issues are, in fact, system issues. That’s not to say the pump is never the cause of the problem; it’s just easy to point to the pump before verifying the system meets the design for which the pump was selected.
Distinguishing between a pump problem and a system problem often requires a good bit of information gathering.
A Methodical Approach
Taco uses a multistep process when identifying issues involving commercial pumps.
The following steps will help ensure technicians are prepared to determine what’s causing the issue, whether it’s handled in-house, or whether to consult the pump manufacturer’s support team.
Usually, troubleshooting support calls come from the rep or customer. When it’s the customer who calls, bring the rep into the conversation before proceeding through the following steps.
1. Stay Calm
The person looking for help may be the engineer or the installer. Regardless, the caller is sometimes panicked. Technicians need to be methodical and collect as much information as possible.
Panicking or jumping to conclusions is not helpful. In fact, jumping to a conclusion is counter-productive, because it may cause a technician to overlook the real issue.
2. Identify the Problem
Here, the caller is asked to briefly explain what’s going on. For example, he may share he has a chilled water system, and the water flow is low. He may insist he’s sure it’s the pump, but that has not been confirmed yet. While a flow problem may exist, it’s cause is unknown at this point.
3. Interview Process
At this point, more information is needed. Specific questions, such as these, need to be asked:
- Is this a water-cooled system?
- If so, is the issue on the chilled water or condenser water side?
- How many pumps are in the system?
- Which model Taco pump is installed?
If it’s not a Taco pump, a member of the Taco team can still help resolve the issue, but the customer needs to understand it’s unlikely technicians will have the pump data on hand. There’s a chance technicians will still identify if there’s something wrong within the system, but without the pump data, a conclusion may not be able to be reached.
Once the pump model data is identified, the design operating conditions must be stated. These are the conditions for which the pump was specified. The actual, real-time pump performance will also need to be identified, allowing technicians to compare design conditions and actual performance information later.
This means someone on-site will be required to measure the flow and pressure drop across the pump. If there are pumps in parallel, it’s best to measure flow across one pump at a time. This establishes individual pump performance.
If the people on-site are reading less flow than design, the tool they’re using to measure flow needs to be identified. The preferred method is a calibrated flow meter, either a permanently installed unit or a strap-on, ultrasonic meter. Measuring the delta-P across the pump is an indicator, but it’s not conclusive.
4. Data Collection
The importance of photographs can’t be overstated. There’s no such thing as too many images. Photos can help determine if the system was piped according to the original design and identify easily overlooked issues, like placement of meters. Collect as many images as possible and develop a file. The earlier these images are available in the troubleshooting process, the better.
Technicians may want to review these images while they’re on the phone with the person who took them. This allows them to navigate the images and ask further questions that may arise.
Technicians also need access to the piping diagrams. If diagrams aren’t available, perhaps a hand sketch exists.
Once images and a diagram or sketch are obtained, the electrical data needs to be collected. Volt and amp readings should be taken at the motor input by a licensed electrician. If the pump is equipped with a variable frequency drive (VFD), the readings should be taken at the input of the drive, not the motor. This is because the VFD modifies the voltage going to the motor.
There are other considerations when a VFD is present on the pump. Ideally, the electrical data at the drive should be taken at full speed. This means the flow and pressure differential must also be measured at full speed.
Make note of the pump’s revolutions per minute (rpm), as this allows technicians to verify the pump is in fact operating at the correct speed and in the correct direction.
The next pertinent item is manufacturer data. It’s quite common for people to think they have pump model X, only to realize it’s a different pump when they send a picture of the pump tag. Photos help confirm the pump model.
After the pump model is known, the single most important piece of manufacturer data is the pump curve. The installation and operation manual is also critical. Next, technicians will acquire field data. Taco calls this the commercial pump troubleshooting report. This sheet is available as a download from Taco’s website. This is the minimum amount of data that should be collected.
5. Analyze the Data
Let’s assume this is a Taco FI Series 5011D. Referencing the pump curve, in a single-pump configuration, this unit provides 1,000 gallons per minute (gpm) at 80 feet of head. The red line represents the pump curve, and the blue line represents the system curve. In this example, the customer didn’t actually measure the flow. Instead, he measured the pressure differential across the pump and reported it was 92 feet of head.
Keep in mind, there’s a correction needed here. The 5011D is an end-suction pump, which typically has a larger inlet than outlet, so the data will need to be corrected for the velocity.
The customer did this, and 92 feet was correct, meaning the pump curve line was intersected at 750 gpm.
Technicians would prefer to have the flow measured independently, so it could be checked either through a permanently installed flow meter or a noninvasive, strap-on, recently calibrated ultrasonic flow meter.
In this scenario, the pump is operating on the pump curve but at a different pressure drop, which hints at a system issue instead of a pump issue. Looking at the pump curve, this unit should be operating at 25 horsepower (hp) while providing 1,000 gpm at 80 feet of head. Given the field-collected flow and pressure, the pump curve shows the pump should be operating at roughly 21 hp.
Determining the actual hp of the pump in the field requires a number of electrical calculations.
The field data recorded by an electrician (at 1,760 rpm) is used to calculate the actual pump horsepower. The efficiency and power factor of the pump is listed on the pump’s nameplate. These numbers are critical components in the calculation.
When the hp in this example was calculated, it was discovered the pump was operating at 21 hp, as expected. This confirmed the reason the proper flow was not occurring was that there’s more system resistance than was originally anticipated.
Next, the technician should ask the people in the mechanical room for the shut-off head. Keep in mind, this number can be greater or less than the published value by as much as 8 feet. To determine the shut-off head, throttle back the discharge valve and isolate it for a few seconds. The operator should be able to measure the pressure differential across the pump. In this case, the shut-off pressure should be around 97 feet, which will confirm the impellor diameter is as specified (10.15 Inches) and indicated on the pump curve.
6. Recommend a Solution
Everything that’s been done so far leads the technician to believe there’s a pressure drop in the system beyond what was anticipated. So, the tech should take another look at the piping diagram and photos. In this scenario, there was only one difference between the piping diagram and what existed in the mechanical room.
The photos revealed a basket strainer installed between the cooling tower and the suction side of the pump. This, the technician learned, was added after the initial installation and was not part of the design. Despite the fact that the published pressure data for the strainer was 2 feet, it was causing a 12-foot pressure drop.
At this point, it was up to the customer to determine what to do about the strainer. Maybe it can be removed, maybe it can be oversized, but, suffice to say, this was not a pump issue.
7. Additional Considerations
There are a few key elements to troubleshooting a pump issue that weren’t discussed in the above example.
The use of a glycol mixture instead of pure water will significantly raise pumping resistance within a hydronic system. The dilution of the glycol, along with the temperature of the system fluid, will have an impact. The more glycol used, and the lower the fluid’s temperature, the greater the resistance.
When measuring the pressure differential across the pump, the difference in elevation between the inlet and outlet gages can have an impact on collected data. If the gages are at different elevations, a correction needs to be made before the readings can be used in any calculations.
Having calibrated gages and meters is the only way to ensure the readings are accurate. Most suppliers of gages and meters will check the calibration of the instruments before shipping them.
There are three types of pressure gages readily available: conventional, compound, and digital. If conventional gages are used, keep in mind the unit will read zero any time the pressure is at or below zero. It’s very unlikely pressure will ever be zero.
Don’t hesitate to ask the contractor to exchange the existing conventional gage with a compound gage. After doing this, it may become evident negative pressure exists at the gage, and the negative pressure may cause the pump to cavitate. As a result, in most cases, it’s better to install compound or digital gages than conventional gages.
As technicians troubleshoot a pump, keep in mind that, more often than not, the pump isn’t the issue. While the pump can be the problem, it’s far more likely there’s an issue with another component in the system, such as a deviation from the engineer’s piping diagram, a faulty component, or an installation mistake.
The best approach to quickly resolve such an issue is to eliminate variables by collecting and reviewing information. The more information and photos that can be referenced, the faster a technician is likely to come to a conclusion.
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