Selecting The Right Spray Pump
Posted by Andrew Greess on Jun 27, 2009
Spray Away! Selecting the perfect spray pump
The pump is the heart of power-spray systems used for pest and weed control, landscaping, golf courses and tree fertilizers. The right pump can make the job a breeze; the wrong pump will quickly ruin your day. And a high-quality pump in the wrong application is a waste of money.
Selecting the right sprayer pump requires answering some important questions:
- What is the application?
- What is the material being sprayed?
- How hard will the pump be used?
- What is the skill level of the applicator?
- What is the ability of the maintenance staff?
- What is the availability of repair/replacement parts?
- What is the budget?
- What is the total ownership cost of this pump?
If you are unsure of any of the answers, get input from staff, colleagues and vendors. NOTE: For this article, I will focus on gas-powered pumps.
1. What is the application?
What volume and pressure are required to do the work? For example, applying a weed pre-emergent doesn’t require much pressure, but significant volume may be required to treat large areas. Spraying 60-foot trees requires high volume and high pressure. Cleaning picnic tables requires pressure, but not much volume.
Higher-pressure pumps are required to reach extreme heights, push material through long hoses, and/or throw material over some distance. Higher-volume pumps may be required to drive booms or boomless nozzles.
Piston/plunger pumps provide high pressure, but not much volume. Roller pumps are great for volume at moderate pressure. Diaphragm pumps can supply both volume and pressure. Centrifugal pumps can provide volume, but not much pressure.
Design your sprayer for its most common use. Many organizations waste money designing a sprayer that handles all situations, but in the field doesn’t handle any application well.
All pump manufacturers provide volume- and pressure-output specifications. Remember that these spec charts are usually maximums at the pump, and actual results at the end of the hose will be lower. Plumbing fittings, valves, constrictions, hoses, distance, pump wear, and extreme temperatures will reduce output. Charts are available to calculate pressure loss through a given size and length of hose. Spec charts also provide horsepower requirements. Be sure to select an engine that can power the pump to provide the results you need.
If using jet agitation in the tank, be sure to consider this when determining the required pump output. Click here for more on jet agitation at Sprayequipmentblog.com.
2. What is the material being sprayed?
If you are just spraying water, this is not really a concern. Generally speaking, granular fertilizers and herbicides are tougher on pumps than other products, such as pesticides. These materials can be corrosive or abrasive, and will significantly reduce pump life if an appropriate pump is not used. If the material is not corrosive or abrasive, there is a lot of flexibility. Diaphragm, piston, plunger, gear, roller or centrifugal pumps may all be appropriate.
If spraying herbicides, the best choice may be a diaphragm pump or a high-end roller pump. If applying granular fertilizers, a diaphragm pump or poly-centrifugal pump may be the best bet. If a pump is not appropriate for the material being applied, you will know it quickly, and the boss will ask why you need another pump so soon.
3. How hard will the pump be used?
If the pump will be subjected to rigorous use, either through long operating hours or by technicians who are tough on equipment, you may want to upsize the pump.
If the pump is barely large enough to provide the required output, it may be running at the high end of its operating range. Most pumps are designed to run “in the red” for short periods only. Running the pump full-out for extended periods will significantly reduce pump life.
My experience is that spray technicians tend to run pumps fast to get the jobs done quickly. If you have a slightly larger pump than needed, you may be able to get longer life and better results. For example, a six-roller pump may provide the output required, but for slightly more money, an eight-roller pump will provide the required output at a much slower speed.
4. What is the skill level of the applicator?
Some pumps are more sensitive than others, so technician skill is critical. For example, a diaphragm pump may be run dry for a short time without causing much damage, but a roller pump run dry will be destroyed in no time. Similarly, gear pumps can be great general-purpose pumps for many applications, but require periodic field adjustment. If you don’t have confidence in spray techs to perform this operation, then a gear pump is not the right choice. Be sure you understand operating requirements before buying a pump.
5. What is the ability of maintenance staff? What is the availability of repair/replacement parts?
A pump requires maintenance, and if not well maintained, it will require repairs. Be sure to understand the maintenance requirements of a pump. What tools are needed? What skills are required? Where does one buy spare parts? Ask these questions in advance, and you will save time, money, downtime and lots of aggravation.
Read the pump owner’s manual to understand and plan for the recommended maintenance. Make sure the required parts are in stock or readily available. I recommend a rebuild on a pump once a year. If a pump is used constantly and you can’t afford downtime, perhaps more frequent rebuilds are in order.
Rebuild a pump at the end of the season or before the start of the next season. Too many organizations wait for the pump to break before doing the repair, which costs time and money and can turn an inexpensive maintenance job into a complete pump replacement. Ouch!
6. What is the budget? What is the total ownership cost of this pump?
Obviously, the above criteria are meaningless without a budget to support them. Generally speaking, diaphragm pumps are the most versatile and the most expensive. If there is not enough money in the budget for everything you want, try to find somewhere else to save money, including talking to an equipment provider. Don’t skimp on the pump--it will cost you. Also, some pumps require larger engines, which can quickly raise the total package price.
Remember, the cost of the pump is not just the price. Consider productivity, maintenance/repair cost, downtime, etc. If you buy the wrong pump and it takes a spray tech twice as long to do a job, have you saved money? Conversely, you may be able to use increased productivity to justify the purchase of a larger pump. If you buy too small a pump or the wrong pump and it always breaks down, you will pay in the long run.