A burner with the two-step pump is a lot easier to work on and set up
In two previous articles we looked at the setting and adjustment of damper motors and the servicing of the linkage on commercial burners equipped with that type of damper. In this article we will take a closer look at one of the pumps that makes these burners operate.
If you remember, I said that both Beckett (CF1400) and Carlin (702CRD) have produced only one burner each using the Suntec two-step pump and, in my opinion, a burner with the two-step pump is a lot easier to work on and set up once you know how everything works. The fact that a single nozzle is used also seems to center the fire better and is one less thing to worry about.
One of the questions that comes up a lot in my classes is why there are not more burners that use this method. I don’t know why there aren’t smaller burners than these two; you’d have to ask the burner OEMs. But I do know the reason why there are no bigger burners. It’s simply because there are only three models of the two-step pumps out there. The Suntec B2TA-8850 can supply oil to the nozzle at 300 psi, or hi-fire, at 10 gph; the B2TA-8851 that can perform the same job up to 16 gph; and the B2GA-8852 that can deliver up to 23 gph.
I guess the place to start would be in the pump itself and to take a look at the basic operation. The pump I’ll be using is the Suntec B2TA8850 and it is the granddaddy of today’s by-pass pumps. The by-pass pump is delivering great performance on residential burners and you will probably see more of these designs in the future. It’s interesting to note that although there are slight differences in operation, all of the “Big Three” are using them. At residential levels they provide for a pre-wash cycle that allows no oil to the nozzle during pre-purge, a smooth and clean light off and a similar shutdown. Overall, a great design.
In Figure 1, I show the flow schematic for the two-step pump. In the bottom half of the picture, the flow circuit for the strainer, the two gear-sets that makes it a two-stage pump, the shaft area, gauge port and bleeder are just about the same as any other Suntec two-stage pump. Where things get interesting is at the top.
On the left side of the drawing, and attached directly to the gear-sets, the schematic shows the pump with the internal oil valve energized and operating at full pressure, normally 300 psi. On the right is the same piston and valve assembly, but the valve is de-energized and so the pump is delivering the lower operating pressure to the nozzle port, normally 100 psi.
It’s a good time to note that in Figure 2 we’ve added an oil valve after the nozzle port with a gauge. That oil valve is critical for safe and correct operation. If you think about it, once the gear-sets come up to speed and the fuel cutoff opens up, you do have oil flow to the nozzle port. The oil valve stops the flow until you want it and in reality it is normally two valves wired and piped in series, making for a redundant system. That redundant-system method is as old as the hills and can be found on burners all the way back to the 1910s, so nothing new there.
When the burner starts, the oil external valve(s) will be closed and the internal pump valve will be open. Until the pump reaches speed, both the fuel cutoff and external valve will remain closed. With the pump at speed, the fuel cutoff will open, but the shutoff oil valve being closed doesn’t allow oil flow to the nozzle. After a pre-purge period, determined by the operating control or timers, the shut-off oil valve will open and there will be lo-fire oil pressure to the nozzle.
Now we need our damper motor to activate and energize the internal oil valve within the pump. As the damper motor operates up to the full air setting, it will activate the circuit we discussed in the first article on damper motors and the valve will close. Up until now, the valve has been open, creating just enough restriction or pressure to regulate lo-fire oil pressure. With the bypass now closed, the pump gear-sets come up to full pressure and deliver the adjusted hi-fire oil pressure.
It’s very important to note that when setting the two operating pressures on the Suntec two-step pumps that the pressure gauge is only in one place and that must be on the pressure side or nozzle port of the pump. The lo-fire pressure is set through the adjustment screw on the top of the pump and valve assembly, and the hi-fire pressure is set through the pump body as it is in most pumps.
The burner should be set up using the OEM’s specifications and then operated through a couple of lo-hi-lo cycles while monitoring the operation and smoothness of transition. Then the burner should be taken to hi-fire and the hi-fire oil pressure verified to specifications. After verifying hi-fire oil pressure, the lo-fire manual switch should be opened to allow the damper motor to de-energize and the lo-fire oil pressure verified.
With the oil pressures verified, adjusted and set for correct operation, and according to the OEM’s specifications, you now should adjust the air according to the OEM’s procedures for both lo- and hi-fires and make final adjustments only with combustion testing equipment and you’re done.
Remember what I said in Part 1 (FON, December 2005) about smoke during transition? I don’t care what it is during transition, just so it’s zero smoke at hi-fire and lo-fire and quiet through the transition.
George Lanthier is the owner of the Firedragon Academy, a teaching, publishing and consulting firm. He is a proctor and trainer for the industry’s certification programs and is the author of nine books on oilheating and HVAC subjects. He can be reached at 132 Lowell Street, Arlington, MA, 02474-2756. His phone is (781) 646-2584; fax (781) 641-7099 and his Web site featuring the industry’s only “trade-only” discussion board can be found at www.FiredragonEnt.com.