Basic Performance Curve-Critical Ejector

at constant load, the discharge pressure is slowly increased. The suction pressure will remain constant until a limiting discharge pressure is reached. 

If the motive steam pressure were reduced slightly, there would be an insignificant lowering of the suction-pressure curve, but the maximum discharge-pressure curve would be shifted downward significantly making the ejector broken at loads below 20 Ib/hr. 

In summary, for a typical ejector stage operating in the critical range, the basic performance curve is essentially fixed. The maximum discharge-pressure curve is somewhat variable, and the ejector will operate on its basic performance curve if the maximum discharge pressure is not exceeded. 

An ejector designed for noncritical operation has somewhat different performance characteristics and these are described in Chapter 18. The performance curve for noncritical ejectors is a function of the motive steam pressure and the actual discharge pressure. Thus, it has no broken mode of operation. 

---

The basic performance curve for an ejector operating in the critical range is determined by fixing the motive steam pressure and the discharge pressure and varying the load to the ejector suction. Corresponding values of suction pressure are observed and the performance curve shown in Figure 23-7 can be developed. 

---