16_pump_assembly_and_testing_tips

16_pump_assembly_and_testing_tips - Pump Assembly and...

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Unformatted text preview: Pump Assembly and Testing Tips You are to assemble and evaluate the performance of your pump. Assembly steps include: 1. Make sure you don’t have any burrs (stray pieces of the gray PVC material) projecting into the impeller cavity that could interfere with your spinning pump impeller. If you see something that could interfere with impeller rotation, you must trim this off before going to the next step. 2. Grease your pump shaft near the o‐ring. Wipe off any grease that gets on the portion of the pump shaft that will interface with the impeller; this grease will reduce the friction between the impeller and shaft, causing the impeller to slip on the shaft. 3. Press your impeller onto the shaft. You WILL break your impeller if you are not extra careful, and you may break it anyway. Apply a uniform pressure to the top of the impeller with your thumb. If you apply even a small force to an impeller blade that is not straight down (in the direction of the pump axis), the blade will snap off. 4. After pressing the impeller into the cavity, the top of the impeller must be below the top of the pump body or else it will contact the face plate and be jammed. If the impeller protrudes beyond the pump body, you must remove it and carefully reduce the height of the impeller by sanding with fine sandpaper (no less than 220 grit sandpaper). When sanding, apply only a very small amount of force to the impeller or it WILL definitely break. You can only remove the impeller by pulling the motor out from the rear of the pump (ask the help desk for more zip ties if this happens). 5. Insert the faceplate o‐ring seal, and tighten four screws. 6. If you break your impeller, check with your instructor or the help desk to see if you can get a spare. The pump may still pump even if it only has one or two blades left. 7. You will have the next class to wrap up loose ends on the pump project, in case you need didn’t finish last time. Reasons Some Pumps Don’t Work: 1. The motor doesn’t spin. If the motor has power and still doesn’t turn, the impeller is probably stuck either by contact with the face plate, the bottom of the pump cavity, the sides of the pump cavity, or with one of the barbed fitting (which could be screwed in too far). If the bronze bushing/o‐ring seal is too tight, this too can restrict impeller rotation. 2. The motor spins but the impeller does not turn. The impeller is probably hung up. However, your pump may still not work when the impeller is freed since a loose connection may be present between the motor shaft and the impeller. If you have a loose impeller / motor shaft connect, you can super glue the two parts together; his usually works, but sometimes extra glue can drain back into the seal (don’t let this happen). If you still have slippage, try a new impeller (with the impeller hole properly sized with a #44 drill bit). 3. Poor pump performance: a. The pump inlet MUST be below the surface of the supply water. This pump is not self priming. b. Sometimes the small diameter inlet hose for the pump will be filled with air, preventing water from getting to the pump. In this case, unplug the pump outlet hose and let water run freely though the pump until the air is gone (with the pump off). c. Pumps sometimes don’t work well because of air trapped in the pump cavity. i. With the pump off, unplug the pump outlet and let water run freely though the pump for a few moments; point the pump exit upward so that the pump remains filled with water. ii. With the pump running, point the pump outlet upward while gently tapping the pump against the floor. This will help to jar and chase bubbles out of the pump cavity. Remember that the pump must remain below the water supply when trying to remove trapped air. iii. The most common source of air leakage is the large o‐ring that provides a seal between the faceplate and pump body. This o‐ring should be lightly compressed against the faceplate and the pump body using the four screws. A small UNIFORM gap should remain between the face plate and pump body when the screws are properly tightened (the o‐ring will fill this gap to prevent leakage). 1. If the faceplate is touching the pump body, you have either over‐tightened your screws OR you have drilled the o‐ring shoulder too deep into the pump body (using the 1.25” diameter Forstner bit). a. If you have over‐tightened the screws, simply unscrew them a little to leave a small uniform gap between the faceplate and pump body. Make sure that the o‐ring is still compressed between the faceplate and pump body. b. If you have drilled the o‐ring shoulder too deep, then do one of the following: i. Use a thicker o‐ring between the faceplate and pump body. Your instructor will have a thicker o‐ring; this is an easy fix. ii. Ask your instructor to have a technician sand away part of the pump body to reduce the depth of the o‐ring shoulder (you must be trained to use a belt sander). iv. Leakage around a barbed fitting is sealed by wrapping threads on the fitting with Teflon tape prior to assembly. v. Leakage around the motor shaft is uncommon and may be caused by one of the following conditions: 1. The motor axis may not be concentric with the pump cavity or the hole drilled on the back side of the pump body (due to improper drilling during pump fabrication). 2. The bronze / o‐ring seal may be defective. Press it out to make sure it looks OK. d. Try swapping the + and – leads to the pump since the impeller may be spinning backwards. e. The pump works best when the exit is drilled on the correct side of the pump body. Students sometimes drill the exit on the wrong side; you can print another impeller with the impeller blades sweeping the opposite direction and swap the + and – on the pump to reverse the direction of impeller rotation. f. The o‐ring may be squeezing too tightly on the DC motor shaft or there may be super glue in the bronze bushing that is restricting motion. If this occurs, you need to remove your motor (cut the zip ties and pull the motor out) and ream out the bushing hole and o‐ring with a #42 drill bit. Don’t worry too much about the drill bit contacting the o‐ring (they seem to seal OK even after drilling). ...
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This note was uploaded on 02/08/2011 for the course ENGR 120 taught by Professor Hall during the Winter '08 term at LA Tech.

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