Especially if you’re dealing with a rugged application, you have questions about submersible pumps. We receive a lot of common questions that we’ll begin to address here. We hope that by sharing them with readers, we can make your selection process faster and easier. We’ll also clarifying some issues you may not have thought to ask. We’ll include additional FAQs in future posts.
How many starts per hour can a submersible pump handle? Can a cast-iron pump handle more than a stainless steel pump?
Before we delve too deeply into this question, let’s first define what “starts per hour” means. It’s the number of times in an hour that a pump starts pumping and then stops. It’s also known as the “duty cycle”. Both stainless steel and cast-iron BJM pumps are rated for ten starts per hour or fewer. Exceeding this number can cause the pump’s motor to overheat; over time, it can burn out the motor completely. Although cast-iron pumps tend to dissipate heat more quickly than stainless steel, neither type should be exposed to excessive cycling.
Too-rapid cycling can result from a variety of factors. For example, if you use an oversized pump, the level of flow the pump provides will overrun the input to the sump. That forces the pump to start and stop repeatedly to keep the level in the sump at the desired level.
Adjusting the float switches to provide a longer runtime reduces the number of starts/stops in an hour. Other options include using discharge valves where appropriate or variable frequency drives (VFDs). However, the best option is to ensure the capacity of the pump matches the requirements of the application.
To find the right pump, always provide detailed information on the system to the pump supplier, including the level of discharge, piping, elbow, and valve types involved. Also, share details on the geometry of the sump (its height, width, depth), fluid levels (full level, empty level), and the speed at which fluid enters the sump. This helps provide a more precise calculation for the gallons per minute requirement to satisfy the starts per hour limitation. If it turns out your system requires a heavy-duty cycle, BJM’s Fahrenheit pumps are a high-endurance pump option to handle it.
Are stainless steel pumps better suited for low pH or high pH applications?
The chemicals (and its concentrations) and solids in the fluid matter more for pump selection. Aggressive chemicals like sulfuric acid and hydrochloric acid corrode cast iron or bronze pump components, and also attack O-rings, seals, and power cable materials. Pumps constructed of plastics, 316 stainless steel, or more exotic alloys may provide greater protection against acidic and caustic chemicals, food processing residues, liquids and by-products.
For insights on which materials can stand up to specific chemicals, consult one of the many chemical resistance charts available, such as Graco’s Chemical Compatibility Guide or Cole-Parmer’s Chemical Compatibility Database.
What’s the maximum fluid temperature to which to expose a submersible pump without a high temperature rating?
Pumps without a high temperature rating handle fluids up to 104°F (40°C), which are common in clean-up applications in food and beverage processing facilities. For temperatures higher than that, BJM recommends switching to one of the Fahrenheit® high temperature submersible pumps, which handle liquid temperatures up to 200°F (93°C). Applications in which these high temperature pumps excel include beverage/bottling plants, poultry/meat/dairy processing and boiler blowdown.
Pumping liquids at temperatures higher than 200°F is inadvisable because water approaching the boiling point will introduce bubbles and create cavitation. When those bubbles pop, they can damage the internal surfaces of the pump over time. By eroding the surface of the impeller, they can create imbalances that lead to mechanical seal failure.
Since 1983, we’ve been designing submersible pump solutions for harsh environments. Our experience allows us to help our customers with specific needs. We’ve also created an online Product Selector Guide to help you narrow down the pumps that will work for your system by answering five questions. Use this helpful guide or contact us directly at 860-399-5937 and we’ll help you get the pump your application demands.