Zenith^® Submersible Pumps

Have you ever come across an application that was too difficult to handle with a standard pump and seal design? Maybe the viscosity of the fluid is too high and there is not sufficient head pressure to push the fluid into the inlet port. Or maybe the process fluid has a tendency to crystallize or is temperature sensitive. If the application calls for pressure below atmospheric conditions, air might get pulled into the pump between the plates or possibly the shaft seal.

Cavitation, crystallization, temperature control, and vacuum service are the main reasons to consider a submersible pump. A submersible pump can eliminate some concerns associated with the traditional style of pump and shaft seal.

Zenith does not recommend installing their pumps in suction lift installations. These installations require the pump to run dry until primed and dry running must be avoided. In certain applications, it is not possible to pressurize the fluid in order to feed the inlet port. The pump may cavitate and eventually fail. However, if the pump is submerged in the process fluid, then the risk of cavitation is virtually eliminated. To enhance the ability of the submerged pump to pull in fluid, the inlet port is enlarged. Any risk of cavitation is removed after having eliminated all restrictions at the inlet.

In other cases, the fluid may be sensitive to air moisture. The vessel holding the fluid is free of contamination and air is replaced with a nitrogen blanket. Any exposure of contamination to the fluid may cause the fluid to have a negative reaction. This type of situation can cause a difficult and more expensive sealing mechanism. In order to protect the fluid from contamination, a double shaft seal with a flush fluid is usually required. The flush fluid is intended to energize both the inboard and outboard seals while protecting the process fluid from external contamination. However, if the pump is submerged in the process fluid itself, the need to use a shaft seal is eliminated. Any fluid that travels through the tight bearing clearances simply reenters the supply tank.

Some applications require that the pump temperature be maintained in a very narrow band. Excessively high temperatures may damage the fluid and excessively low temperatures may cause the fluid to return to a solid state. Holding the pump at a certain temperature can be difficult with fluid or even electrical heater controls. Submersing the pump into the process fluid, which is held at the proper temperature, eliminates the need for pump temperature controls.

Vacuum service has always been somewhat difficult for a Zenith pump. Zenith pumps use a metal-to-metal seal between each plate. The flatness and smoothness of the plates makes a great liquid seal and prevents fluid from leaking out of the pump. Unfortunately, under vacuum conditions, this type of seal is not very proficient at preventing gas from entering the pump. Any scratches, blemishes, or lack of parallelism in the plates may result in gas entering the pump. This problem may cause a loss in pump efficiency and introduce gas bubbles downstream. By submersing the pump into the process fluid, the only media that has the possibility of getting pulled between the plates is the process fluid. This eliminates the gas bubbles entering the process and also improves the efficiency of the pump.

Because the pump is submerged in the process fluid, the drive system must be altered in order to engage the pump shaft. The most common method is to couple the pump by using an extended drive shaft. Depending on the application, the shaft would pass through the cover of the vessel down to the pump. The pump can be fixed to the bottom of the vessel or by supports attached to the lid which allows the pump to be removed when the lid is taken off of the vessel. For vacuum service or for fluids pressurized with a blanket, a shaft seal is used.

This type of pump and drive system is ideal for preventing cavitation, eliminating shaft seal land temperature control issues, and avoiding gas from entering the pump even under vacuum. Shown below are a few examples of where submersible pumps have been used with great success.

Two-Component Urethanes:

Urethane products like pre-polymers and catalysts are typically fluids that are better handled with a submersible pump. These type of fluids contain isocyanates that harden when exposed to air/moisture. The pump can be submersed and the fluid can be metered directly from a drum or containment vessel without the risk of problems associated with shaft seals. Some polyol pre-polymers (partially catalyzed) are high viscosity fluids. The inlet pressure to the pump must be increased in order to prevent cavitation. Using a submersible pump with a large inlet port prevents cavitation from occurring.

Molten Sulfur:

Our last news letter featured an application story for pumping molten sulfur. The sulfur must be heated to a very specific heat range in order to be transformed from a solid to a liquid. Too high a temperature degrades the product while too low a temperature would return the sulfur to its solid state. Heating the pump and maintaining a tight temperature range with a fluid or electric heat jacket is a difficult task. However, by submersing the pump into a vessel, the pump is held at the same temperature as the process fluid. All concerns for effectively heating the pump have been eliminated.

Molten Solder:

Solder is another application which is very similar to molten sulfur. Solder is basically a blend of at least two metals such as lead and tin. The melting temperature is about 360°F (182°C). Using an H-series high temperature pump submersed in the molten metals allows the fluids to be pumped while eliminating any concern of the pump seizing due to improper temperature control.

Submersible pumps are ideal for a number of difficult pump applications. Problem areas such as cavitation, vacuum service, contamination and controlling pump temperature can be eliminating by using a submersible pump. Please contact our Application Engineering Group to determine if a submersible pump may be the solution to some of your difficult pumping applications.