Product Overview | Differential Pressure Ratio Regulator
7288 Regulators are used as flow balancing air/gas ratio control devices in air primary systems. The 7288 matches pressure drop across an orifice in the gas line to the drop across an orifice in the combustion air line, thereby matching gas and air flows from high fire to low.
5D
3D
5D
Gas
1807
3 psi Max. Inlet
Standard arrangement uses an 1807-type limiting orifice valve as the gas orifice, adjusting it for desired air/gas ratio.
Max. ( P) Pressure Drop 20"wc
Differential pressure ratio regulators represent the least expensive method of ratio control on applications where resistance and/or backpressure varies in the air and gas lines downstream of the orifices. WHY FLOW BALANCE Many heat recovery installations require flow balance ratio control because resistance in the air line increases as recuperator or reclaimer temperature rises. The 7288 system works on the principle that matched differential pressures mean matched flows (assuming air and gas temperatures are maintained at each orifice). For example, as a recuperator's temperature goes up and air flow through it is restricted, pressure drop across the orifice plate in the cold air line decreases. The 7288 senses this and reduces pressure drop across its orifice (usually a limiting orifice valve), thus decreasing gas flow in the same proportion as the air flow reduction. Preset air/fuel ratio is maintained. Accurate turndowns of 7:1 or more can be realized if pressure drop is appropriate across the air orifice at high fire. MULTIPLE BURNERS More than one burner can be fed by a single 7288 Regulator as long as individual burner adjustments, once set, are not altered or do not change inadvertently due to burner air or gas orifices plugging or individual downstream resistance changing from other causes. (The 7288 will maintain ratio if both gas and air are shut off on individual burners.) In multiple burner set-ups, the main benefits of the 7288 control can be realized on some installations by venting the downstream gas connection. The Regulator then maintains an outlet static pressure in proportion to the differential pressure across the air orifice. Consult North American about the practicality of this arrangement for a potential application.
Air
Air Control Valve
10D
per orifice mfgr's specs.
Table 1.
CAPACITIES cfh with 2 osi drop through regulator
Regulator designation
Gas gravity
0.4
0.6
1.5
7288A-0 7288A-1 7288-2 7288-3 7288-4 7288-5 7288-6 7288-7
300 500 1000 1500
250 400 800 1200 2400 4000 6000 11000
150 250 500 775
3000 5000 7350 13400
1500 2500 3800 7000
(for capacities at other pressure drops, use square root law or Table 2 on this bulletin).
Table 2. Capacity correction factors for various pressure drops across 7288 Regulators (see Table 1).
Pressure drop, osi
Pressure drop, osi
Factor
Factor
1
0.707
8
2.00 2.24 2.45 2.65 2.83
2 3 4 6
1.00 1.22 1.41 1.73
10 12 14 16
*Assuming there is no hot air bleed in the recuperator system.
(16 osi is maximum recommended drop)
Bulletin 7288 Page 2
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