Tweaking your "D" valve for Reduced Steam Consumption

Steam Happens 27

Scotch Yoke Animation

 

Click here for my movie showing a Scotch Yoke water pump

*****************************************************************

Note that at 50% of travel crankpin is always at 90 degrees to stroke axis

***********************************************************************************************************************

Note that the longer the stroke the larger the angularity issue

********************************************************************************************************************

Note that longer connecting rods tend to lessen angularity issues

***************************************************************************************************************

Note that introducing cutoff produces angularity issues that are unequal on the outstroke and return stroke

**************************************************************************************************************

Diagram 5: Comparing Scotch Yoke and Connecting Rod Engine for Angularity Error

Note that, unlike the connecting rod engine, the crank motion in a Scotch Yoke engine always produces equal angularity for the down-stroke

and return-stroke

*************************************************************************************************************

****************************************************************************************************************************************

****************************************************************************************************************************************

Tweaking the HasBrouck #1 Engine's "D" valve for Improved Efficiency and Smoother Running.

An Example that will give you some practice before you modify your own engine.

*******************************************************************************************

 

 

FIGURE 1: HasBrouck #1 Steam Chest & D Valve

**************************************************************************************************************

FIGURE 2: HasBrouck #1 Original D Valve Dimensions

**************************************************************************

FIGURE 3: Crankpin and typical eccentric position

******************************************************************************

 

FIGURE 4:  Eccentric position showing typical advance angle

****************************************************************************

LET THE TWEAKING BEGIN: The valve design software, Valvegr2.xls, can be found for download at

http://earlmorse.org/steamboa.html

****************************************************************************

FIGURE 5:  Inserting HasBrouck's Original Dimensions into Will's Tweaking Software

The original HasBrouck dimensions (in red) replace the original (black) included in the software.

Top value (e.g. admission lap = 0.031) refers to downstroke, the value beneath it (also 0.031) refers

to the return stroke. Note that the original software's advance angle is left at 38 degrees for the

time being.

*******************************************************************************

FIGURE 6: This results in an admission of -31 degrees Before TDC. To get the admission to 0 degrees

38 is added to the -31 resulting in an advance angle of 7 degrees (see below).

This produces TDC and BDC admissions of 0 degrees.

********************************************************************************

FIGURE 7: Zeroing admission to TDC and BDC shows almost no cut-off in original HasBrouck specs.

***********************************************************************************

FIGURE 8: Adding to the original HasBrouck the lap specs of 0.031 to try a lap of  0.125 inches

but now the admissions are 23 degrees after TDC and BDC. So we'll add 23 degrees to 7

degrees to bring admissions to TDC and BDC and make the advance angle 30 degrees.

(within the typical advance range of 30 to 38 degrees)

************************************************************************************

FIGURE 9: First tweaking brings cut-offs to the 70-80% range

**********************************************************************************

FIGURE 10: Adding a bit to the advance angle and the laps produces better results, but now the return

cut-off is too much.

***********************************************************************************

FIGURE 11: Changing the return admission lap to 0.135 inches brings the return cut-off to nearly

62% of travel.  It turns out that -4 degrees early admission of the return stroke is OK.

Having a -4 to -2 degree early admission on the return stroke makes for an easy starting and

smooth running. This is because a very small amount of piston movement represents a large

amount of rotation at BDC (because of angularity), which effectively gives a large amount of

leverage over the steam force on the piston. 

************************************************************************************

 

FIGURE 12: Visualizing port opening sizes. 

BTW, Will likes a bit of exhaust lap (0.031 inches in this case) in his engines since it

"cushions" piston direction reversal, quiets slightly worn bearings a bit, and helps reduce

the use of steam in the next incoming charge. Exhaust lap is less important in small engines

and/or engines with sealed ball bearings. It's your call.

****************************************************************************

FIGURE 13  HasBrouck #1 Modified Dimensions After Tweaking