Modified single-shaft turbopump incorporates inducer and main pump, each separately driven at different speeds through coaxial-shaft arrangement. Inducer operates at low speed for low net positive suction pressure, main pump operates at high speed to generate high pressure. This arrangement requires no external control for the inducer

Bair, E. K.

Campbell, W. E.

Ford, O. I.

English

NASA Technical Reports Server

December 1970	 Brief 70-10671 
NASA TECH BRIEF 
-0 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
Virginia 22151. Requests for individual copies or questions relating to the Tech Brief progam may be directed to the Tech-
nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Twin-Spool Turbopumps for "Low" Net Positive Suction Pressure Operations 
Pump Speed = 22,000 rpm
NPSP = 7 psi 
,_
 
	
NPSP=5psi	 'N 
1 /	 I	 • I! 
NPSP=Opsi 
1i.i. 
5
800 
a, 
cc 700 
600 
500 
c 400 
300
Inducer Shaft 
0 10 20 30 40 50 60 70 80 90 100

Flowrate, Lb/sec 
Figure 1. Effect of NPSP on Single-Spool Turbopump Performance 	 Figure 2. Twin-Spool Turbopump Schematic 
The problem: 
Rocket engine turbopumps capable of operating at 
low to zero net positive suction pressure (NPSP) would 
improve rocket engine performance and reliability. 
Specifically, the need to pressurize propellant storage 
tanks could be at least simplified or possibly elimi-
nated. [NPSP is the margin by which total pressure in 
the pumped fluid exceeds its vapor (saturation) pres-
sure, as measured in the supply tank. Low or zero 
NPSP is achieved when the absolute pressure in the 
supply tank approaches or equals the saturation pres-
sure of the fluid.] Figure 1 indicates the reduction in 
performance of a conventional single-spool turbo-
pump as the NPSP is reduced to zero. 
The solution: 
A separately driven low-speed inducer, capable of 
handling the pumped fluid at low NPSP and raising 
its pressure to an adequate NPSP before it is ingested 
by the main-pump inlet, is employed. The twin-spool
turbopump, Figure .2, incorporates the inducer and 
a main pump, each separately driven at different 
speeds through a coaxial-shaft arrangement. The in-
ducer can operate at low speed for low NPSP, and the 
main pump can operate at high speed to generate 
high pressure. This arrangement results in a minimal 
envelope and requires no external control for the in-
ducèr. 
How it's done: 
The twin-spool turbopump is a modification of a 
single-shaft turbopump in which a centrifugal pump is 
driven by a two-stage impulse turbine. The single-
shaft turbopump is modified to add an in-line, low-
speed inducer immediately upstream of the main pump 
inlet, and an inducer drive turbine immediately down-
stream of the main turbine, with the inducer drive 
turbine extracting its power from the main turbine 
exhaut. The inducer and the inducer drive turbine 
are mechanically connected by a shaft that is coaxial 
(conlinued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
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with the hollow shaft connecting the main pump and 
the main turbine. Both the inducer and the main stages 
are supported by their own rolling-element bearings. 
A twin-spool hydrogen turbopump for pumping 
liquid hydrogen at zero NPSP has been developed and 
tested. This turbopump operates satisfactorily over 
its entire operating range with zero NPSP at the inlet 
of the low speed inducer. The stall margin of the pump 
does not drop when the pump is operated at low posi-
tive suction pressures. The twin-spool turbopump 
makes the fuel system pressure rise insensitive to varia-
tions in tank pressure, thus hydrodynamically decoup-
ling the tank from the engine. 
Notes: 
1. The twin-spool turbopump can be used in pumping 
applications where low NPSP is desired. 
2. A computer program which accurately predicts 
both steady-state and transient operating character-
istics of the twin-spool hydrogen turbopump has 
been developed. This computer program is available 
from: COSMIC, Barrow Hall, University of 
Georgia, Athens, Georgia 30601. Reference: LEW-
11079.
3. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA- CR-72540 (N69-36246), Investigation 
of Twin-Spool Turbopump Performance 
Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: TSP70- 10671 
Patent status: 
No patent action is contemplated by NASA. 
Source: 0.1. Ford, W. E. Campbell and E. K. Bair of 
Aerojet-General Corp. 
under contract to 
Lewis Research Center 
(LEW-1 1105)
[1 
Brie!' 70-I 0671	 Category 07


Twin-spool turbopumps for ''low'' net positive suction pressure operations

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