Paxman History Pages - RPH and YH engine versions

RPH and YH Engine Versions (Mark Numbers)

Paxman's most successful (in terms of numbers sold) and best known range of 7" bore engines was the RPH series. Over 6,690 were built; more than any other type of Paxman engine. Important applications of the RPH included rail traction, driving generator sets including marine auxiliaries and emergency or standby sets, marine propulsion, oil well drilling and powering Ruston-Bucyrus excavators.

The earliest version, the RPH Series 1 range, was derived from the wartime 12TP and was virtually the same engine. Edward Paxman, son of the Company's founder, announced to the Board in November 1942 his plans for an in-line six cylinder 7" bore x 7¾" stroke engine called the RPH. This was basically a 12TP with one bank of cylinders blanked off. RPH engines were ordered in November 1944 for eight Royal Navy Daring Class Destroyers, as auxiliaries for electrical power generation. It seems likely that industrial (i.e. non-defence) sales of the RPH did not really take off until about 1947. The Paxman Sales Engineers' Handbook says of the RPH Series 1: "Many hundreds were produced between 1947 and 1954, in six and twelve cylinder versions, both normally aspirated and pressure charged." (1)

In 1951 Paxman commenced production of the vee form RPH Series 2. This had greatly improved accessibility and incorporated a number of technical advances such as increased bearing areas, gear-driven water pumps and roller cam followers. Initial production centred on twelve and sixteen cylinder sizes, both normally aspirated and pressure-charged. (2) During its production life the RPH Series 2 appeared in a number of versions or 'Marks'. This page charts the changes to the RPH, and to its direct-injection successor, the YH, which were introduced during their production lives. A more general history and description of the RPH and YH engine ranges can be found on the page Paxman Diesels since 1934.

A summary of the main changes to RPH and YH engines, up to c.1967/68, was published in the Paxman Sales Engineers' Handbook in chart form (3), the text of which is reproduced in the table below.

Designation (Engine Nameplate)	Maximum Continuous Speed, r.p.m.	Description
RPH Series 1	1,250 †	Immediate post-war production. (Conversion sets were also supplied for war-time TP engines.) 6 (in-line), V6 and 12 cylinder normally aspirated and pressure charged engines.
RPH Series 2	1,250 †	Present basic version RPH. Introduced 1951. Engine range increased to 4, 6, 8, 12 and 16 cylinder models: 16 cylinder subsequently withdrawn, 1961.
RPH Mark 3	1,250	As for RPH Series 2 but including the following features: Alfin pistons, hardened valves and seats and other small modifications. Production started 1958.
RPH Mark 4	1,500	As for Mark 3 but including the following features to permit continuous operation at 1,500 r.p.m.: Nimonic hot plugs, "E" type connecting rods, and oil cooling to pistons, balance weights on 12 cylinder engines. Production started. 1958.
RPHX Mark 5 RPHC Mark 5 (4, 6 and 8 cyl. only)	All speeds up to 1,500 r.p.m.	Pressure-charged version of RPH Series, using "Holset" air cooled turbo-blower, oil cooled pistons, larger fuel pump plungers and modified inlet and exhaust manifold: other components remain the same as normally aspirated versions for interchangeability. Production started, 1960.
12RPHX and 12 RPHC Mark 5	1,250	Pressure-charged version of 12RPH Series, similar to 4, 6 and 8RPH Mark 5 engines. Engine without crankshaft balance weights. Production started, 1961.
12RPHX and 12 RPHC Mark 6	1,500	Pressure-charged version of 12RPH Series, similar to 4, 6 and 8RPH Mark 5 engines. Engines with crankshaft balance weights. Production started, 1961.
RPH, RPHX and RPHC Mark 7	1,500	As for Mark 5 & 6 but with low compression pistons, new ring arrangement and pintaux injectors (RPHX & RPHC), connecting rods common to all engines, aluminium main and large end bearings (not for blade rod), increased capacity oil pumps and sump (12 cylinder), new water transfer system - cylinder block to head (4, 6, 8-cylinders), intercooler mounted under turbo-blower (4, 6, 8RPHC). Production started 1970. 4-cylinder engines withdrawn 1970.
YHA YHAX	1,000 1,000	Design evolved for Admiralty (ASR2). Introduced 1952. Engines similar to RPH Series 2 but including the following features: engine combustion system and cylinder heads re-designed for direct injection, wet type cylinder liners, lightweight materials. 6 (in-line) and 12 cylinder normally aspirated and pressure charged engines.
YHX Mark 2* YHC Mark 2*	1,250	Basic version of YHX for commercial purposes, introduced 1957. Main features as for 1,000 r.p.m. version but with smaller turbo-blowers, individual fuel injection pumps. 6, 12 and 16 cylinder pressure charged engines.
YHX Mark 3* YHC Mark 3*	1,250 (1,500 r.p.m. for 16YHX & C)	As for Mark 2, but with modifications to maintain interchangeability with RPH Mark 3. "E" type connecting rods and oil cooled Alfin pistons standard for all speeds. Production started in 1958. 6 and 12 cylinder sizes withdrawn in 1960 and replaced by Mark 4 versions.
YHX Mark 4* YHC Mark 4*	1,500	6 and 12 cylinders only. The same as Mark 3 but with air cooled turbo-blower, block type fuel injection pump and re-designed cambox and drive. Balance weights fitted at speeds over 1,250 r.p.m. Introduced, 1959. 6 cylinder model withdrawn 1961.
ZH ZHX	1,500	Horizontal in-line engine evolved from the YH design for underfloor mounting in railcars. Introduced 1954.

† Engines have been supplied at higher operating speeds than those quoted for specially approved applications of an intermittent nature.
* Lightweight versions are also available for Admiralty applications only (withdrawn for commercial applications May 1964) and are designated AYHXA and AYHCA.

COMMENT from Don Meiklejohn: There was a RPH Mk 6 as per the above chart. This was a 12 cylinder turbocharged engine running at 1,500 rpm. To run at this speed the 12 cylinder engine required the fit of a crankshaft fitted with balance weights. This shaft was the one fitted in 12YH engines. The remainder of the engine was however basically the same as other 12RPH Mk 5 engines and normally most people would have called it a "Mk 5".

(Author's Note on the Paxman engine notation system: RPH or YH with the suffix 'X' indicates that the engine is turbocharged but not intercooled. The suffix 'C' indicates that the engine is turbocharged with air to water intercooling. Paxman's notation system is described in detail on the page Identifying Paxman Diesel Engine Types.)

Subsequent Changes

Changes introduced in subsequent Marks of the RPH Series 2 and YH ranges were detailed in Technical Data Sheets (TDSs) issued by the Company in September 1970. The text of these TDSs is reproduced below with additional comments from Don Meiklejohn, Senior Technical Support Engineer at MAN Diesel & Turbo UK Ltd, Colchester.

Technical Data Sheet - No. TDS.B1/1 (RPH Mk 7 and YH Mk 6)

Date. Sept. 1970 Issue No. 1
Scope: RPH & YH ENGINES

Subject: Uprated 7 inch Bore Engines - Mark Numbers

A detailed history of the mark numbers for 7" bore engines is given on page 19 of the Sales Engineers Handbook (revision 3) but for recipients of this bulletin who are not issued with the Handbook brief details of previous mark numbers are given below:-

Engine	Aspiration	Speed - rev./min.	Mark No.
4, 6, 8, 12 RPH	Normal	Up to and including 1250 rev./min.	3
4, 6, 8, 12 RPH	Normal	Above 1250 rev./min.	4
4, 6, 8, RPHX and RPHC	Pressure charged with and without intercooling	All speeds	5
12 RPHX and RPHC	ditto	Up to and including 1250 rev./min.	5
12 RPHX and RPHC	ditto	Above 1250 rev./min.	6
12 YHX and YHC	ditto	All speeds	(Holset turbo-chargers) 4
12 YHX and YHC	ditto	All speeds	(Napier turbo-chargers) 5

Engines of the 7" bore range have been modified to incorporate the latest design changes and Value Analysis recommendations. Changes in engine build due to speed (i.e. balance weights on 12 cylinder engines above 1250 rev./min.) and variations in compression ratio between naturally-aspirated and pressure-charged engines will now cease to exist.

RPH, RPHX and RPHC Engines

These engines will now be known as Mark 7.

YHX and YHC Engines

These engines will now be known as Mark 6.

All mark numbers will be written in the form above, not as Roman numerals (i.e. Mark 6 NOT Mark VI).

Details of engine modifications and revised power outputs will be given in a later Technical Data Sheet.

COMMENTS from Don Meiklejohn:
a) This TDS mentions a 12YH Mk 5. There is no "Engineers List" for such an engine and as far as I know no production engines were ever built and supplied to customers. It may however have been a design exercise and could have been run on development as a modification to a Mk 4 engine. Napier Turbochargers were owned by English Electric and this could have been an exercise after Paxman was taken over by EE in 1966.
b) The RPH Mk 7 and YH Mk 6 were introduced to the market in 1969 with the first production engines being built in 1970 and 1971.

Technical Data Sheet - No. TDS.B5/1 (RPH Mk 7)

Date. Sept. 1970 Issue No. 1
Scope: RPH, RPHX & RPHC ENGINES

Subject: Introduction of Mark 7 Engines

This bulletin releases for sale the uprated version of the pressure-charged intercooled RPHC and a revised build standard for normally-aspirated RPH and pressure-charged RPHX engines. Mark numbers for these engines were released through TDS.B2.

The RPHC version has been developed to give 10% more power than existing engines in the speed range 1,000 - 1,500 rev./min. RPHC engines operating below 1,000 rev./min. can only be offered at existing outputs. There is no increase in the rating on RPH and RPHX engines. This uprating has been achieved by reducing the compression ratio to 15.5:1 (from 17.25:1) and re-matching the exhaust gas driven turbo blowers.

Other design changes and value analysis proposals are being incorporated in the uprated RPHC engine and also in the RPH and RPHX engines.

The startability of RPHC and RPHX engines is unaffected as Pintaux nozzles are being fitted to counteract the deterioration caused by the reduction in the compression ratio.

Component changes necessary to achieve the uprating are:-

Deeper combustion bowl in the piston to give a 16:1 compression ratio to keep firing pressures within acceptable limits.
Pintaux nozzle.
Turbocharger (internal components only in 6, 8 and 12 RPHC).

Other design changes and value analysis proposals include:-

Pistons with .125 inch width parallel top compression ring and one oil control ring, all above gudgeon pin. Round wire circlips to locate the gudgeon pin.

Intercooler mounted underneath the turbo blower at the drive end of the engine giving improved accessability in the vee and more robust fixing for the cooler.

Modified free end cover.

Upset forged push rods.

New studs for main bearings, cylinder block and head.
The cylinder heads of 4 and 8 cylinder engines have been strengthened.

Standard (instead of special flanged) nuts for cylinder heads.

RPH Mark 7 - Naturally-Aspirated Engine

This engine embodies all the relevant modifications listed above including the .125 inch width compression piston ring, but the compression ratio of 17.25:1 has been retained. Low speed engines (below 1251 rev./min.) have high speed type rods with an oil supply to the gudgeon pins but with the oil squirt to the piston undercrown blanked off.

RPHX Mark 7 Pressure Charged Engine

This engine embodies all the relevant modifications listed above. The compression ratio has been reduced to 16:1 to maintain maximum interchangeability with the RPHC engines. This is contrary to the statement in TDS.B1 paragraph 4. It has been established that about 80% of all RPH engine sales are for RPHX and C engines. Pintaux nozzles will be fitted.

Heat Dissipation

Specific heat dissipation rates - gross water and oil flows are unchanged.

Fuel and Oil Consumptions

Initial testing indicates that specific fuel consumption remains unchanged at the B.S. continuous rating. New consumption figures will be issued for other duties when sufficient production engines have been tested. Lubricating oil consumption with revised piston ring layout is not affected.

Special Notes for Sales and Contracts

Despatch dates for the uprated engines should be established by the normal D.P.R. procedure. A week is required by Development Department to check the performance on the first production engine of each size and speed.

Load Acceptance

The ability of the engines to accept full load and the overload stop setting is laid down in TDS.A13.

Interchangeability

A complete interchangeability chart will be issued by Engineering. However, the following main components or assemblies are interchangeable with engines built to Mark 3 to 6 standards:-

Liners, normally-aspirated pistons (in sets) complete with rings, gudgeon pins and circlips, main and large end bearings, connecting rods, camshaft, free end gear drives, crankshaft, balance gear, fuel injection pumps (not couplings), governor and linkage, cylinder heads and blocks when modified by fitting a small sleeve, oil pumps.

Outputs

The revised outputs are detailed in the relevant pages of T.D.S. Section A.

Technical Data Sheet - No. TDS.B11/1 (YH Mk 6)

Date. Sept. 1970 Issue No. 1
Scope: 12YHX & YHC ENGINES

Subject: Introduction of Mark 6 YH Engine

This Data Sheet gives technical release for the uprated version of the pressure-charged intercooled 12YHC engine. The mark number for the engine was released through TDS.B2. The output of pressure-charged YHX engines has also been increased.

The 12YHC version has been developed to give 10 - 16% more power than existing engines in the speed range 1,000 - 1,500 rev./min. 12YHC engines operating below 1,000 rev./min. can only be offered at existing outputs. There is also an increase in the rating on 12YHX engines up to 1,250 rev./min. This uprating has been achieved by reducing the compression ratio from 14.25:1 to 13:1 and by fitting a camshaft with tangent shaped cams giving faster inlet and exhaust valve opening and closing rates.

The compression ratio and other components of the YHX engine will be changed to give common parts with the 'C' engine.

Reducing the compression ratio to 13:1 will affect starting by 12°F but this should still enable cold starts to be made down to about 37°F without external aids.

Component changes necessary to achieve the uprating are:-

Piston with larger and deeper valve cut-outs to give a compression ratio of 13:1.
Camshaft with tangent cams to give faster inlet and exhaust valve opening and closing rates.
The Holset 6-1205-303 turbo blower is common for all speeds within the speed range of 1,000 - 1,500 rev./min. The compressor wheel has been redesigned to withstand the higher stresses produced by the increase in boost pressures and rotor speeds.

Other design changes to reduce cost and overcome service problems include:-

Two intercoolers mounted on the inlet manifolds at the drive end of the engine.
New cylinder block giving increased water space and stiffened liner.
Increased capacity (pressure and cooling) lubricating oil pumps.
Re-designed relief valve.
Re-designed reducing valve.
30° inlet valves.
Re-designed sump to take increased capacity lubricating oil pumps.
Aluminium tin main and large end fork bearings.
The following piston ring layout -
The top piston ring has been changed from a 3/16" taper ring to an 1/8" parallel ring.
The oil control ring at the base of the skirt is deleted and the oil control ring above the gudgeon pin is reduced from 1/4" to 3/16" wide.

Heat Dissipation

Specific heat dissipation rates are expected to be unchanged; water flows are unchanged and lubricating oil pump flows are increased by 27%.

Fuel and Oil Consumption

Initial testing indicates that the specific fuel consumption at the new B.S. continuous ratings are unchanged at 1,500 rev./min. and have been reduced by 2% (max.) for speeds of 1,200 and 1,000 rev./min. New consumption figures will be issued for all duties when sufficient production engines have been tested. Lubricating oil consumptions have been reduced by the introduction of the revised piston ring layout (see paragraph 6(i) for description). New figures will be issued when production engines have been tested.

Special Notes for Sales and Contracts

Load Acceptance

The ability of the engines to accept full load and the overload stop setting is covered by TDS.A13.

Outputs

The revised outputs are detailed in the relevant pages of T.D.S. Section A.

COMMENT from Don Meiklejohn: There was an RPH Mk 8 engine. This was based on the Mk 7 but replaced the indirect injection cylinder head and piston with a new direct injection head and a piston with a combustion bowl. I recall this engine running on development testing, it was either a 6 cylinder or an 8 cylinder. It was intended to give a 10% increase in power output over the Mk 7 combined with an improved fuel consumption. In addition a simplified 12 cylinder engine was proposed. This had a redesigned crankcase to take cylinder blocks and heads based on those fitted to the 6 cylinder engine. The fuel pumps were to be on a cross-drive box similar to that fitted on the 4, 6 and 8 cylinder engines. The Mk 8 however never made it into production as there were major problems in getting the exhaust smoke levels acceptable. Even if it had entered production it probably would not have sold well. Our traditional British shipbuilding market was disappearing rapidly due to competition from the Far East and it would have been too expensive for the standby generator-set market where there were a number of newer and cheaper competitors available. These killed off the 12YH sales.

Reference

1. Paxman Sales Engineers' Handbook, published c.1967/68, p.17.
2. ibid, p.17.
3. ibid, p.19.

Acknowledgement: I am deeply indebted to Don Meiklejohn, Senior Technical Support Engineer at MAN Diesel & Turbo UK Ltd for providing much of the information shown on this page.

Page updated: 21 FEB 2014