One observation is companies ask for a specific size of pump because they rented one in the past and it worked. But that does not necessarily mean the same pump is what was needed in a different situation. Once, a jobsite had an 8-inch pump with 8-inch suction and discharge hose hooked up to a 4-inch butterfly valve with a reducer on the front of a frac tank. The pump was cavitating badly due to the restriction of flow, but the crew working there did not seem to notice because it was focused on getting work done.
The misapplication of the pump could have been due to someone’s insistence for that size of pump, or could have been an innocent mistake on the part of the rental company by not asking the right questions to understand the application. In either case, the customer loses. But the next pump can be rented with peace of mind by knowing the answers to a few simple questions. Here are eight questions to review with a rental provider to determine the best pump for the job.
1. What kind of liquid is being pumped?
There are instances when it is just assumed that water is being pumped. But actually, it could be a cocktail of water and other chemicals that are not compatible with the pump or the pipe/hoses used on the pump, causing leaks and costly equipment damage.
2. What is the total suction lift?
Suction lift is the difference between the level of the liquid being pumped and where the eye of the impeller is located on the pump. It is important not to measure only from the level of the water to the surface, as most trailer-mounted diesel or electric pumps’ volute centerline is two-and-a-half to three feet from the ground. This may not seem like a big deal, but for applications where the liquid is 25 feet from the surface, adding the additional couple feet can be the difference between whether a pump will prime or not. The rental advisor should know to add two to three feet to the total lift number.
3. What flow rate is needed?
The speed a user may wish to pump may not be feasible based on where the liquid is being discharged. Many times, the water is pumped into a storm drain, but there could be limitations on what gallons per minute (gpm) is allowed. (Be sure to check local regulations for any discharge permits required; an issue addressed later in the article.)
4. How far away is the discharge area?
The farther the distance, the more friction loss that occurs inside the pipe or hose being used. If the liquid is pumped a mile away vs. 500 feet away, a different pump or larger discharge hose or pipe may be required to give you the flow rate you need.
5. Are there any elevation gains or losses between the pump and discharge area?
A discharge pipe that is on fairly level ground from start to finish makes it easy enough to spec out which pump is needed. But if there are significant elevation gains or losses to account for, those need to be known. Big gains in elevation mean more work for the pump, and thus more power required. Large elevation losses could lead to high rates of velocity and could cause pipe damage.
6. How close will the pump be to the liquid?
A good rule to remember is the closer the pump can be to the source, the better. When determining the total dynamic head (TDH) of the pumping application, less total dynamic suction head (TDSH) is more. Longer distances of suction hose can cause suction cavitation and thus poor pump performance.
7. What is the temperature of the liquid?
People may want to assume ambient temperature, but if there are any doubts, purchase an inexpensive laser temperature gun and confirm. As the water becomes hotter, vapor pressure starts to change, and the liquid becomes more difficult to pump. Pay special attention to this when working with liquids that could be downstream of manufacturing plants, hospitals or other industrial sections of town.
8. Is the final discharge area open or closed and if closed, what pressure needs to be overcome?
Is fluid being pumped into an open pond or storm sewer, or connecting to another pipe onsite that is currently pressurized? If pumping into an existing system, make sure to check if there is pressure in it. If yes, provide that information when speaking to a rental advisor, as it can change the size of pump needed.
There is one more important thing to consider that is often overlooked or forgotten: Are there any state, local or federal regulatory requirements that need to be adhered to before discharging water from the worksite? Remember that environmental laws are in effect, and ignorance of these regulations does not grant a pardon for not following them.