Peter S
Diamond
- Joined
- May 6, 2002
- Location
- Auckland, New Zealand
A while back there was a posting about a derelict ferry in the USA; the steam engine was described as a “double compound”. I had never heard of this type of engine, and still can’t find much info. Anyone have any experience with this type, and how they fit into the last years of the steam reciprocating engine? Some of my ideas below probably need correction please let me know
One problem is the varied descriptions used - when searching the internet I came across what I would call a compound engine (i.e. 1xHP, 1xLP cylinder) described as a “double compound”. For example there is a surviving steam ship called “Segwun”, photos appear to show a compound engine (two cylinders, two cranks), but it is described as a “double compound”. As if life weren’t complicated enough
It took a bit of figuring out, but a marine double compound seems to have four cylinders on four cranks on a common crankshaft. Of additional interest is that they sometimes use the Woolf cycle – revived and employed in some of these last steam engines built. There seem to be different versions, but one type has two pairs of Woolf compounds (i.e. cranks of each pair at 180 degrees), on a common crank, with 90 degrees between the pairs. This allows the engine to always start (no dead centre) while retaining the simplicity possible with cranks at 180 degrees, .e.g. no receiver, one valve per pair of cylinders.
Arthur Woolf was one of the early builders of compound engines; he built his first in 1803. A distinctive feature of the original ‘Woolf’ system (as fitted to beam engines) is that the pistons of the HP and LP work together in the same direction, thus the HP exhausts directly into the LP, no receiver is required between the cylinders. The marine engines described above have pistons working in opposite directions, but being at 180 degrees, I believe it is the same system. The same cycle can be used with tandem and annular engines.
Other types of two-crank compound used a receiver and separate valves between the cylinders; this allows the cranks to be at any position (expansion not dependant on piston phasing). Often cranks are at 90 degress for easier starting and better balance. This popular compound receiver system developed into the triple expansion with cranks at 120 deg, best known of all marine engines.
I suppose another type of “double compound” is the twin tandem engine. Found both on land and at sea, the LP and HP of each pair share the same crank pin. A modified Woolf type became popular at sea – tandem with separate valves for each cylinder. Several such tandem units could be mounted on a common crank to make some of the largest marine engines ever made. However, it is really the four crank types that I am interested in here.
I found descriptions of a few double compound engines as used in the 1920’s-50’s:
W.A. White in the UK developed the White “New Economy” engine which first appeared in 1934, a double compound with HP and LP cranks at 180 deg, each pair at 90 deg, “easy handling and good balance” being the description applied. This engine was a little unusual in being ‘high speed’ (250/300 rpm), it drove the prop shaft via a reduction gear. The LPs’ exhausted into a LP turbine which also drove the prop shaft via the same reduction gear. This unit developed 1230 hp.
(A whole other subject; this type of ‘combination’ machinery was popular and successful in the 20th century and made in many interesting different types by many manufacturers (i.e. using single and double compound, triple expansion, etc. etc. and low pressure exhaust turbines powering geared or hydraulic drives, AC or DC generators driving motors connected to the shaft or electric elements re-heating the receiver steam, compressors re-compressing the receiver steam etc. etc.)
Christiansen & Meyer from Germany made double compounds (Woolf compound), four cylinders, just one valve (piston type) per pair of cylinders. The HPs’ were counterflow, the LPs’ were relieved compression uniflow. Only one eccentric per pair of cylinders, a very simple engine.
Lentz-valve engines were also made double compound from the 1920’s, Woolf-type with no receiver, steam exhausting from HP to LP through a common valve. Once again, HP and LP cranks in each pair at 180 deg, with each compound section joined with HP cranks at 90 deg.
I have a photo showing a Lentz-type double compound engine built in Australia after WW2 for their “D-class” ships. It is fully enclosed and the description says “individual poppet valves”, so maybe not the common valve of the earlier type.
Anyone have info on US or other double compounds?
One problem is the varied descriptions used - when searching the internet I came across what I would call a compound engine (i.e. 1xHP, 1xLP cylinder) described as a “double compound”. For example there is a surviving steam ship called “Segwun”, photos appear to show a compound engine (two cylinders, two cranks), but it is described as a “double compound”. As if life weren’t complicated enough
It took a bit of figuring out, but a marine double compound seems to have four cylinders on four cranks on a common crankshaft. Of additional interest is that they sometimes use the Woolf cycle – revived and employed in some of these last steam engines built. There seem to be different versions, but one type has two pairs of Woolf compounds (i.e. cranks of each pair at 180 degrees), on a common crank, with 90 degrees between the pairs. This allows the engine to always start (no dead centre) while retaining the simplicity possible with cranks at 180 degrees, .e.g. no receiver, one valve per pair of cylinders.
Arthur Woolf was one of the early builders of compound engines; he built his first in 1803. A distinctive feature of the original ‘Woolf’ system (as fitted to beam engines) is that the pistons of the HP and LP work together in the same direction, thus the HP exhausts directly into the LP, no receiver is required between the cylinders. The marine engines described above have pistons working in opposite directions, but being at 180 degrees, I believe it is the same system. The same cycle can be used with tandem and annular engines.
Other types of two-crank compound used a receiver and separate valves between the cylinders; this allows the cranks to be at any position (expansion not dependant on piston phasing). Often cranks are at 90 degress for easier starting and better balance. This popular compound receiver system developed into the triple expansion with cranks at 120 deg, best known of all marine engines.
I suppose another type of “double compound” is the twin tandem engine. Found both on land and at sea, the LP and HP of each pair share the same crank pin. A modified Woolf type became popular at sea – tandem with separate valves for each cylinder. Several such tandem units could be mounted on a common crank to make some of the largest marine engines ever made. However, it is really the four crank types that I am interested in here.
I found descriptions of a few double compound engines as used in the 1920’s-50’s:
W.A. White in the UK developed the White “New Economy” engine which first appeared in 1934, a double compound with HP and LP cranks at 180 deg, each pair at 90 deg, “easy handling and good balance” being the description applied. This engine was a little unusual in being ‘high speed’ (250/300 rpm), it drove the prop shaft via a reduction gear. The LPs’ exhausted into a LP turbine which also drove the prop shaft via the same reduction gear. This unit developed 1230 hp.
(A whole other subject; this type of ‘combination’ machinery was popular and successful in the 20th century and made in many interesting different types by many manufacturers (i.e. using single and double compound, triple expansion, etc. etc. and low pressure exhaust turbines powering geared or hydraulic drives, AC or DC generators driving motors connected to the shaft or electric elements re-heating the receiver steam, compressors re-compressing the receiver steam etc. etc.)
Christiansen & Meyer from Germany made double compounds (Woolf compound), four cylinders, just one valve (piston type) per pair of cylinders. The HPs’ were counterflow, the LPs’ were relieved compression uniflow. Only one eccentric per pair of cylinders, a very simple engine.
Lentz-valve engines were also made double compound from the 1920’s, Woolf-type with no receiver, steam exhausting from HP to LP through a common valve. Once again, HP and LP cranks in each pair at 180 deg, with each compound section joined with HP cranks at 90 deg.
I have a photo showing a Lentz-type double compound engine built in Australia after WW2 for their “D-class” ships. It is fully enclosed and the description says “individual poppet valves”, so maybe not the common valve of the earlier type.
Anyone have info on US or other double compounds?