In selecting a cleaning tool for a specific job, and to operate the tool on a specific jetter or sewer combination truck, the operator must know the variables of flow (GPM), pressure (PSI), hose size (diameter in inches), and hose length (feet), and type of hose - thermoplastic or rubber. All of these variables interact to affect the performance of a sewer cleaning tool. Improper use and alignment of these variables will not allow the tool to perform correctly or will adversely affect the operator's ability to accomplish his/her job.
Flow Rate Versus Pressure
Flow (measured in GPM) is a vital component of the cleaning process. Generally, lower flows as generated by a pump are used to clean smaller diameter pipes, and flow in GPM typically increases as the diameter of pipe increases. Conversely, pressures generated by the tool (measured in PSI) are usually higher when cleaning smaller diameter pipes, and pressure in PSI usually decreases as the diameter of the pipe increases. The table following shows general rules-of-thumb for flow and pressure combinations, and minimum and maximum flows per hose size*.
|| 3,000 PSI
|| <=80 GPM
Tier One, Tier Two, and Tier Three Nozzles
The National Association of Sewer Service Companies (NASSCO) divides sewer cleaning nozzles into three categories (see NASSCO Jetting Code of Practice or visit NASSCO's website on-line at www.nassco.org). Each category has its design and performance characteristics.
Tier One - Nozzles or cleaning tools that have a drilled orifice for creating pressure and have a flat inner surface for receiving and /or redirecting water flow to the orifices are Tier One. The flat inner surface is not efficient from a fluid mechanics perspective. Tier One nozzles are the least expensive to purchase, but also provide lesser performance than the other strata of nozzles. A buyer of Tier One nozzles would be driven by first cost, not product performance or longevity.
Tier Two - Nozzles or cleaning tools that have a replaceable threaded insert or a more rounded inner surface for water redirection are Tier Two. Tier Two nozzles provide a longer service life due to the replaceable threaded inserts provided, and often have better fluid mechanics than Tier One. A buyer of Tier Two nozzles would be driven by greater concern for performance and longer service life of the equipment.
Tier Three - Nozzles that have a replaceable threaded insert and a more rounded, higher efficiency inner surface for water redirection are Tier Three. A buyer of Tier Three nozzles would be driven by total owning costs (performance, durability) rather than first cost.