Why reverse a grinder? by Jason Fletcher

Why Reverse a Grinder? by Jason Fletcher, PE
By now everyone knows the 6840 grinder pump is reversible. But why is this so important? Those who have seen the grinder display cart know the importance of reversibility. This article will try to explain why every grinder job should be reversible. First, let’s review why we use a grinder system. The purpose of a grinder system is to cut-up solids in the wastewater to small particles (typically ź” to ž” or less) that can be passed through the pump, valves, and piping without clogging. Since the solids are ground up, pump discharge sizes can also be reduced. Smaller piping can be used which lowers the flow rate needed to achieve the proper cleaning velocity. This, in turn, allows the electric power consumed by the pump to come from a residential service entrance. Pumps are designed to provide higher heads at moderate to low flows, as required by the hydraulics of pressure sewer systems. Grinder pumps are typically designed to cut common household items, such as: rags, diapers, tissue, panty hose, gloves, sewage, and toiletry items. When an item is introduced to the system that will require more than one pumping cycle to pass then the item is typically wound up on the cutter. This is sometimes referred to as ‘roping’. This usually occurs on items that are long (>12”) or bulky (>12”x12”). When the item is wound on the cutter the pump could either 1) continue to operate but at a reduced efficiency or 2) stop operating. Let’s look at both of these possibilities. First, if the pump continues to operate then the system will continue to empty the basin, but the run time usually increases due to a partially clogged intake and less flow rate. Second, the pump could stop operating. This would be due to an increase in amperage usually tripping the pump’s internal overload caused by a locked rotor condition or increased resistance on the cutter. If a system is not capable of reversing the wound up material on the cutter will stay there. The material may eventually come undone after repeated cycling and decomposition, but will more than likely end up a service call (very expensive). If the pump can reverse then the amount of time required to clear the material will be greatly reduced. Each time the pump runs a little more material can be unwound and sucked into the pump. Within a few cycles the material can be cleared (less service calls). When one tries to remove two components from each other and they are stuck, what is the first thing they do? Usually it is try to turn the parts in the opposite direction. This is done to loosen up whatever may be holding the pieces together. The same is true for a reversing grinder. If the pump jams, it is much easier to clear the jam if the pump is turned in the opposite direction than trying to go the same way. Another benefit to reversing a grinder pump is increased pump life. Since the cutter is now using both sides of the cutter blade the life of the cutter is doubled. This means the cutter stays sharp to do the job for a much longer period of time. That translates to less service calls because dull cutters do not cut but jam up when needed. Now that we understand why we need to reverse a grinder, how does the 6840 pump system meet these requirements? First, the pump was designed with hydraulics that give the same performance when operating in either direction. Second, the pump was given a cutter system that cuts the same in either direction. Third, the controls on the automatic reversing feature were designed such that every time the pump goes off, the pump will come back on rotating in the opposite direction. It does not matter if the pump went off due to cycling of the floats or tripping on overload because of a jam, when it comes back on the rotation will be in the opposite direction. As you can see a quality reversing pump such as the Zoeller 6840 will reduce the operating and maintenance cost of any grinder system.

Why Reverse a Grinder?
by Jason Fletcher, PE

By now everyone knows the 6840 grinder pump is reversible. But why is this so important? Those who have seen the grinder display cart know the importance of reversibility. This article will try to explain why every grinder job should be reversible.

First, let’s review why we use a grinder system. The purpose of a grinder system is to cut-up solids in the wastewater to small particles (typically ź” to ž” or less) that can be passed through the pump, valves, and piping without clogging. Since the solids are ground up, pump discharge sizes can also be reduced. Smaller piping can be used which lowers the flow rate needed to achieve the proper cleaning velocity. This, in turn, allows the electric power consumed by the pump to come from a residential service entrance. Pumps are designed to provide higher heads at moderate to low flows, as required by the hydraulics of pressure sewer systems.

Grinder pumps are typically designed to cut common household items, such as: rags, diapers, tissue, panty hose, gloves, sewage, and toiletry items. When an item is introduced to the system that will require more than one pumping cycle to pass then the item is typically wound up on the cutter. This is sometimes referred to as ‘roping’. This usually occurs on items that are long (>12”) or bulky (>12”x12”). When the item is wound on the cutter the pump could either 1) continue to operate but at a reduced efficiency or 2) stop operating. Let’s look at both of these possibilities. First, if the pump continues to operate then the system will continue to empty the basin, but the run time usually increases due to a partially clogged intake and less flow rate. Second, the pump could stop operating. This would be due to an increase in amperage usually tripping the pump’s internal overload caused by a locked rotor condition or increased resistance on the cutter. If a system is not capable of reversing the wound up material on the cutter will stay there. The material may eventually come undone after repeated cycling and decomposition, but will more than likely end up a service call (very expensive). If the pump can reverse then the amount of time required to clear the material will be greatly reduced. Each time the pump runs a little more material can be unwound and sucked into the pump. Within a few cycles the material can be cleared (less service calls).

When one tries to remove two components from each other and they are stuck, what is the first thing they do? Usually it is try to turn the parts in the opposite direction. This is done to loosen up whatever may be holding the pieces together. The same is true for a reversing grinder. If the pump jams, it is much easier to clear the jam if the pump is turned in the opposite direction than trying to go the same way.

Another benefit to reversing a grinder pump is increased pump life. Since the cutter is now using both sides of the cutter blade the life of the cutter is doubled. This means the cutter stays sharp to do the job for a much longer period of time. That translates to less service calls because dull cutters do not cut but jam up when needed.

Now that we understand why we need to reverse a grinder, how does the 6840 pump system meet these requirements? First, the pump was designed with hydraulics that give the same performance when operating in either direction. Second, the pump was given a cutter system that cuts the same in either direction. Third, the controls on the automatic reversing feature were designed such that every time the pump goes off, the pump will come back on rotating in the opposite direction. It does not matter if the pump went off due to cycling of the floats or tripping on overload because of a jam, when it comes back on the rotation will be in the opposite direction. As you can see a quality reversing pump such as the Zoeller 6840 will reduce the operating and maintenance cost of any grinder system.