If the liquid you’re pumping contains solids, there are a number of solids handling submersible pumps that might be appropriate for your application. To avoid clogs or burning your motor out, you need to make sure you have the right pump. There are key questions that help determine which pump will solve your problems. In this post, we’ll examine these questions so that you’re prepared when you talk with your provider.
1. What Type of Solids Are You’re Pumping?
Understanding the solids in your liquid helps your provider determine the right type of pump for your application. We’re focusing on wastewater, so we can assume your solids are not abrasive (abrasive solids would require a hard metal, agitator pump). Most likely, they are large and soft or long and stringy. You also need to know if the solids need to be reduced to go into your system or to discharge, or if you just need to pass them.
Understanding the type of wastewater is also helpful. These are generally categorized as municipal (including sewage) or industrial. While municipal wastewater is generally consistent among sites, industrial wastewater solids and contaminants often vary based on industry.
2. What Solids Loading Can the Pump Handle?
There needs to be enough liquid either in the sump or in the system to keep solids moving with the liquid. Without enough water, the pump will clog and won’t be able to pass the solids. Most solids handling pump designs can handle approximately 5% solids by volume. If your wastewater has a higher concentration, you will likely need to add more water to the sump by changing the system to allow more water to accumulate in the sump or by adding more water to the process.
The sump pump basin size is also a factor. The basin should be sized to minimize the number of cycles per hour but cannot be so large that solids will settle instead of being brought into the pump.
3. How Might Your Piping System Affect the Pump You Need?
Understanding the design of your piping system will help your provider make sure there are no areas where the solids may settle, build up and cause clogs. This includes:
- Size of the Piping: It must be large enough to pass solids downstream, but small enough to maintain carrying velocity to prevent solids from settling out. We recommend carrying velocity of 5-7 ft./sec. for municipal wastewater applications. As the specific gravity of the solids increases, you may need to further increase the velocity to carry the solids.
- Vertical Lift: This is the height that water has to travel as it moves through your piping system. A significant vertical lift combined with an improperly sized pump can cause solids to recirculate and clog within the pump volute.
- Location of Check Valves: The check valves should be as close to the pump as possible. If too far from the pump or too high, solids can build up before reaching the valve. This causes clogging as the solids backflush into the pump. Adjusting the location of the check valve generally solves these issues.
In some instances, your provider may conduct an inspection. If the entire piping system isn’t visible, you may need to show the piping system plans or explain where and how far the piping goes. The piping connections and fittings are important too.
4. What Is the Required Flow Rate for your System?
The flow rate is the amount of liquid that runs through the system in a given amount of time. This and the pipe sizing determine the velocity needed to pass the solids downstream through the pipes. The flow rate also indicates the appropriate size your sump should be. An undersized sump causes the pump to cycle too frequently and burn itself up.
If you don’t know your flow rate, here are two options to help your pump provider determine it:
- Calculate the flow rate by performing a draw down test. With no water entering the sump, allow the current pump to run for as long as possible while recording the time in operation. The flow rate is the volume of liquid pumped (sump length x sump width x the change in liquid level from start to end of pumping cycle) divided by the amount of time recorded during the drawdown test.
- If you have the model number of your current pump, researching the pump’s performance curve combined with the piping system information or a pressure gauge reading in the system can help your provider calculate the flow rate.
Translating Answers to the Solids Handling Pump You Need
The answers to these questions provides the information your provider needs to make a recommendation. The natures of the wastewater and solids determine the type of pump you need (i.e. shredder or vortex pump). The flow rate (and the amount of head in the system) indicates the specific pump model you need.
In addition, you may have unique circumstances to consider, especially when dealing with harsh environments. These are the types of situations in which BJM Pumps excels. We build submersible pumps to deal with rugged applications and have 35 years of experience helping customers dealing with the issues you deal with every day. Contact us or call us at 860-399-5937 to request more information or to initiate a personalized evaluation of your submersible pump needs.