Within a wastewater treatment or water treatment plant, a screw pump moves all of that liquid at a constant speed in the most efficient way possible. Screw pumps are designed to avoid clogging and excessive wear. They don’t require much maintenance, but that doesn’t mean they never experience issues. Here’s a list of common screw pump problems and how to resolve them.
What Is a Screw Pump?
Before getting into common screw pump problems, it helps to know how they work. There’s a giant screw inside a trough or pipe that continually rotates. As it does, water pushes from the bottom of the screw to the top with the help of momentum, the screw’s ridges, and the sides of the trough or pipe. This moves liquids from a lower point like a pool or wet well to a higher point like a basin or tank.
What Issues Are Common?
What are the most common issues people experience with their plants’ screw pumps? These six issues are the most likely to occur.
Cavitation
Sometimes, pressure changes in liquid form small cavities, and then allow vapor and gases to fill those pockets that implode. This is known as cavitation and occurs when the static pressure is lower than the liquid’s vapor pressure.
Why does cavitation occur? If there is insufficient suction pressure, it’s common. Having high fluid viscosity or gas and air in the fluid are other causes.
When cavitation happens, it creates vibrations that can damage the mechanics within the pump and lead to the failure of the bearings, seals, or shaft. It’s important for the pressure at the suction portion of the pump to remain steady. Reduce the pump’s speed and increase the level of fluid in the suction tank. If gas or air are present, remove them before the liquid makes it to the screw pump.
High Pressure With the Discharge of Liquids
A high discharge pressure is often tied to a blockage in the discharge line. It also occurs if the valve is closed. Those can be easy fixes. Find the blockage or open the valve. It also occurs if the pump speed is set too high. Again, it’s an easy fix.
Leaks
Leaks also create noises as the fluid levels being moved through the screw pump aren’t adequate. You should notice leaks as you’ll find fluid where it shouldn’t be. They usually occur when seals are worn or fittings are loose. The repairs for leaks involve replacing worn or damaged seals and tightening or replacing loose or broken fittings.
Loss of Flow or No Flow
If your system is not pushing water at all or the flow rate has greatly diminished, it’s often a sign that your motor is working too slowly or is overloaded. It can be tied to a loose belt if the pump is belt-driven. It can also be tied to insufficient suction or the suction pipe being inadequately sized. If the fluid pressure is too close to or matches the vapor pressure, it can lead to issues with flow. If the viscosity of the liquid is too high or the liquid is too hot, flow rates are also impacted.
When any of this is happening, the motor needs to be examined. Make sure everything is lubricated correctly, that belts are tight, and that a variable frequency drive is set correctly. Check the fluid’s temperature and viscosity, and change speed and suction rates if needed.
Loud or Excessive Noise
Is your screw pump making loud rattles, bangs, or grinding noises? Those are not normal noises and need to be investigated. A screw pump makes noise, but excessive or extremely loud noises are not okay.
Loud or excessive screw pump noise is a sign of a clog, cavitation, blocked suction or discharge, misalignment, or worn or damaged bearings. If there are problems, have the repairs made ASAP. Alignment may need to be adjusted. Any blockages need to be cleared.
Make it a point to know how a maintained, properly functioning screw pump sounds. The easier it is to identify the normal noises, the easier it is to determine when a noise isn’t the same.
Overheating
While the maintenance of a screw pump is minimal, you still need to make sure the pump components are lubricated and working properly. When there is too much friction, overheating is possible and damages a pump in a short time.
Overheating is often linked to operating pumps at too high a speed, clogged lines, or air leaks within the system. All three of these possible causes have to be addressed.
If you are running your pump faster than is needed, slow it down and see if the problem goes away. Check the lines for clogs, and look for air leaks. Finally, check the lubrication levels and make sure there is adequate lubrication within the pump.
Don’t Delay Troubleshooting Issues
Never delay your attempts to troubleshoot issues. If there is a problem and you wait too long, the repairs could become far more costly. Identifying issues in the earliest stages can save money in the long run. Especially if you have a screw pump expert like Lakeside Equipment to help with the repairs.
Most problems are avoidable if you perform routine maintenance on your screw pumps. You should always keep an eye out for leaks or unusual noises. If there are any concerns, call in an expert. It’s better to pay for an inspection and learn nothing is wrong than to wait and have your pump fail and need to be replaced.
Two Types of Screw Pumps
When you’re investing in screw pumps in your plant, there are open and enclosed screw pumps. Enclosed screw pumps have the screw installed within a solid pipe. Open screw pumps are in a concrete or steel trough.
Lakeside Equipment offers two types of enclosed screw pumps: Type C or Type S. Type C has a smaller horizontal footprint and an outer rotating tube, while Type S has a stationary tube with a pivot feature to reduce the maintenance needs on the lower bearing. There’s no grouting work required, so installation costs are lower.
Open screw pumps don’t clog, so you don’t need to pre-screen your wastewater. Installation doesn’t require a wet well, and maintenance is minimal. But, they’re going to require a lot of concrete, steel, and possibly grout to build the troughs.
Which is right for your plant’s needs? Talk to the experts at Lakeside Equipment about your goals and plant design and we’ll help you figure out the right solutions for your budget, volume, and space.
