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with Sentry Rotator
An Innovative and Patented Mechanical Valve Rotator for 2-Stroke Engines. Your Engine. Our Ingenuity.™ Märkisches Werk GmbH
MWH Americas
MWH China
58553 Halver, Germany Phone: + 49 - 2353 - 917 - 0 MWH Japan
Email: [email protected] Your Engine. Our Ingenuity.™ 10/29/13 6:38:10 PM

MWH ReliaValve with Sentry Rotator MWH ReliaValve with Sentry Rotator Engines operating with eco-speed or extreme low- steaming down to 10% load experience high valve DESIGN OF CURRENT EXHAUST spindle temperatures caused by the lower cooling effect of the scavange air (low scavange air Two-stroke engine exhaust valves operate under VALVES AND WEAR MECHANISMS pressure follows low load). In addition, the specific extremely harsh thermal and environmental lubrication quantity under low-load conditions is conditions that typically result in a 6,000 - 8,000 hr. A large fraction of the world's marine 2-stroke high. The low sulphur content of the fuel (HFO) service interval for these components [1]. engines are designed by three manufacturers: results in an over-abundance of calcium from the Exposure to high temperatures and heavy fuel oil MAN-B&W (MC-Series), Wärtsiläe-Sulzer (RTA- lubeoil. Under these conditions, the possibility of (HFO) combustion products can lead to severe series) and Mitsubishi (UEC-series). Each engine creating glassy-deposits on the seat area of the chemical attack on the valve head and other parts design has unique features, but many general valve-spindle becomes high when the correct seat of the exhaust system. Eco-speed and low characteristics of the exhaust system are common contact pressure is present. Build-up of glassy- steaming can reduce engine speeds down to 10% to all three manufacturers. Figure 1 shows a deposits on the seat of the bottom piece has not load. Combined with the additional low sulphur typical 2-stroke exhaust valve assembly, including requirements, these conditions can promote rapid the valve drive (hydraulic actuator), pneumatic wear of the valve spindle seat surface. MWH has spring (air cylinder), valve housing, valve guide, These glassy-deposits (see Figure 4) have a seen by-products of the combustion with ashes of valve spindle (with vane rotator), and bottom piece Figure 2: Valve guide with evidence of
hardness of approximately 800 HV with high non-burning constituents coming from the HFO as adhesion and abrasive wear [6].
adhesion to the valve seat material. During well as from the lubeoil. inspection, it is only possible to remove the glassy- Wear Mechanisms in 2-stroke Engine Exhaust Macro particles and dent marks refers to a deposits from the valve spindle seat with hard This paper describes the design, testing and serial mechanism in which particles and deposits formed metal scrapers. Different coefficients of thermal operation of a novel mechanical valve rotator for as a by-product of the combustion of fuel (HFO) expansion between the valve spindle seat and the increasing the service life of 2-stroke engine The most prevalent wear mechanisms in 2-stroke become trapped between the valve spindle and glassy-deposits lead to radial cracks in the deposit engine valves have been described in [2] and seat ring. When the valve spindle closes on the layer. These cracks are the initation of exhaust gas seat ring, these particles generate a ‘dent' in each channels. After a channel is formed, and a blow • Adhesion and abrasive wear of the paired surfaces. Repeated denting of the through begins to develop, the local temperature • Macro particles and dent marks seating surfaces can eventually create a path for increases, accelerating the local corrosion and • Build up of glassy-deposits leakage of combustion gases. Once this occurs, causing rapid removal of the metal surface itself • Low temperature corrosion the hot combustion gases lead to the rapid erosion [3]. Typical so called "cobblestone" corrosion [4], • High temperature corrosion and corrosion of these metal surfaces. Figure 3 characteristic of high-temperature corrosion is • Low-cycle fatigue shows a photograph of a valve spindle with documented in Figure 4 as type of valve spindle extensive evidence of dent marks. wear. Subsequent valve spindle failure usually The first two of these wear mechanisms (adhesion/abrasive wear and macro particles/dent marks) are of particular interest to this project, and are described in further detail. Adhesion and abrasive wear refers to a mechanism in which deposit particles can become entrapped between the valve guide and valve spindle stem. These particles adhere to the valve spindle guide and cause abrasive wear on guide Figure 3: Valve spindle with extensive evidence
and stem. This mechanismen causes a sticking of dent marks [6].
effect which can prevent rotation of the valve spindle. Lack of rotation causes un-symmetric Recently, we have begun to see a new type of heating and distortion of the valve spindle head, wear mechanism on the valve spindle seat, the so which can subsequently lead to combustion gas called "glassing" or "glassy-deposits". As opposed Figure 4: Valve spindle with extensive "glassy-
leaks and erosion. Figure 2 shows a photograph to the well known wear mechanism from macro- deposits" and beginning of blow-byes.
of a valve guide with considerable deposit particle particle indentation (see Figure 3), these glassy- deposits form a thin, hard layer only on the valve Analysis of Glassy-Deposits spindle seat surface. The mechanism of the glassy deposit formation is very complex and appears to MWH analysis of the glassy-deposits showed the be related to a combination of the following presence of compounds of calcium, vanadium, sulphur and sodium. Under pressure and temperature, the salts crystallize to form a thin • Fuel (HFO) quality glassy layer. Kingston-Jones, et al. have described • Lubeoil quality and quantity the formation of low melting point salts in detail [5]. • Engine operation condition Sulphur oxides (SO 2 and SO3), vanadium oxides • Seating pressure 2O5) and sodium oxides (NA2O) from the combustion process react with each other and with Figure 1: Typical 2-stroke engine exhaust valve
calcium from the lubeoil to form these low melting MWH ReliaValve with Sentry Rotator MWH ReliaValve with Sentry Rotator point salts. These salts include sodium sulphate An innovative and patented mechanical valve DESIGN FEATURES OF THE 4), calcium sulphate (CaSO4) and sodium rotator (Sentry Rotator) for 2-stroke engines has vanadyl vanadates of varying compositions MECHANICAL VALVE ROTATOR been developed by Märkisches Werk GmbH (usually referred to as NaVV). Table 1 shows a list Various approaches for controlling wear in exhaust (MWH). This valve rotator mechanism can be of sodium vanadyl vanadates and their respective valves have been employed with various degrees incorporated into an existing exhaust valve of success. This paper describes the design of a assembly with only minor modification, as shown in mechanical valve rotator that addresses both of Figure 6 and Figure 7. The rotator features an the aforementioned wear mechanisms to extend inner and outer drive element. The helical rotating Table 1: Melting points of some vanadates [5].
the service interval of 2-stroke exhaust valves. gear is linked to the inner drive element via a free- The main benefit of mechanical rotation is wheel device that transmits a rotation to the valve stem during the valve closing movement. The achieved when a certain wiping or grinding effect is helical gear rotator and free-wheel mechanism are produced on the valve spindle and seat ring shown in Figure 8. surfaces. This seating surface polishing effect is produced by the valve spindle's rotational motion as it contacts the bottom piece or seat ring [5]. Figure 5: Valve spindle with extensive
dentmarks and beginning of blow-byes (W-type
geometrie of bottom piece).
Conventional Valve Rotation Mechanisms Rotation of the valve spindle within the exhaust valve assembly is beneficial for several reasons, *NaVV = sodium vanadyl vanadate 5:12 = 5Na and it generally reduces the wear rate of the exhaust valve assembly. Today, most 2-stroke 1:6 = Na2O.V2O4.5V2O5 exhaust valves rely on aerodynamic vanes (wing bushes) for passive spindle rotation (see Figure 1). Exhaust gases flow over the vanes and rotate the Seat Ring Geometry spindle as it opens, creating an axi-symmetric temperature distribution, and reducing thermal The three different designs of the seat of the gradients within the valve spindle. This decreases bottom piece of 2-stroke exhaust valves were distortion and thermal stresses within the spindle, described extensively in [6]. The standard-type and reduces low and high cycle fatigue. However, design features flat valve spindle and seat ring in some types of engines, vanes fail to provide Figure 7: Detail view of mechanical valve
surfaces, while the W-type and Chamber-type seat additional important benefits, namely the polishing rotator mechanism.
rings employ a more complex geometry with the and removal of residuals on the valve spindle aim of addressing the dent mark wear mechanism. sealings surface and overcoming the stiction These seat ring designs generate higher interfacial caused by deposits within the valve guide. As contact loads, and provide a pocket where cool, discussed previously, these phenomena lead to un-combusted gases can reside next to the seating wear of the exhaust spindle, guide and seat ring, surface. If a passage for gas leakage is created by and ultimately force most operators to service their dent marks, the cool gases can escape without exhaust valves after 6,000 to 8,000 hours of eroding the metal surfaces of the valve spindle and service. The rotation rate of the spindles is not controlled with the use of aerodynamic vanes. As Seat ring geometry modifications can be used to a result, inadequate rotation is achieved at low alleviate the dent wear mechanism, but the engine speeds and loads, and insufficient adhesion and abrasive mechanism (sticking of rotational torque is generated to overcome stiction valve spindle stem) and blow-byes (glassy- within the valve guide once adhesion and abrasive deposits) must be addressed by other means, see wear are initiated. Positive mechanical rotation also Figure 4 (chamber-type) and Figure 5 (W- addresses the shortcomings of traditional valve Figure 6: Exhaust valve assembly with
Figure 8: Helical gear rotator and free-wheel
mechanical valve rotator.
mechanism.
MWH ReliaValve with Sentry Rotator MWH ReliaValve with Sentry Rotator Advantages of Mechanical Rotation surfaces on the valve spindle and bottom piece were performed. In 2007, the inspection showed The mechanical valve rotator essential y forces a that the continuous rotation described above was controlled rotation of the valve spindle during the effective in maintaining clean, polished seating valve closing movement. This continuous rotation surfaces. Moreover, no dent marks were visible on speed can be tuned from 3 – 20 rpm, and is a either the valve spindle or bottom piece surfaces. linear function of the engine speed. In addition, this Even after 16,647 hours of operation, there was no valve rotation is achieved even under conditions evidence of excessive wear on the seating where sticking in the valve guide would prevent rotation with an aerodynamic vane. The Sentry Rotator provides all the traditional Based on the postive results seen in 2007, the benefits of valve rotation, including an axi- target of 30,000 hours service-free operation was symmetrical temperature distribution in the valve deemed as possible. Additional to the on-going spindle to reduce thermal stresses and improve field test on six MAN-B&W engines in the range low and high cycle fatigue life. However, by from MC60 to MC90 type, there are also nine rotating the valve spindle during the closing MAN-B&W engines completely equipped with movement, a continuous polishing effect is converted ReliaValves. With this wide range of achieved on the seating surfaces of the valve experience, the MWH ReliaValves have been spindle and bottom piece. This seat polishing approved for 30,000 hours or more. The only effect prevents deterioration by dent marks and scheduled maintenance item for the ReliaValve dramatically reduces the possibility of combustion with Sentry Rotator consists of the replacing the gas leaks. In essence, continuously polishing the valve spindle stem seals after 15,000 to 18,000 seating surfaces ensures that al functions of the hours. This work can be performed on board seat (gas sealing, heat transfer, etc.) remain at without removing the complete ReliaValve from Figure 12: Photograph of the valve spindle and
peak efficiency throughout the life of the engine. the engine. Only disassembly of the valve drive and air cylinder is necessary to change the stem seat ring surfaces after 16,647 hours [6].
An additional possible benefit is that, by removing sealings. It is recommended that the free-wheel Figure 10: Photographs of the valve spindle
the aerodynamic vane (wing bush) from the valve mechanism and axial bearings of the Sentry and seat ring surfaces after 1,000 hours [6].
spindle stem, an improvement in scavenging Rotator be inspected every 30,000 hours and efficiency may be achieved. This could result in replaced, if necessary. improved thermodynamic efficiency of the engine and reduced fuel consumption. However, this effect has not yet been quantified. Mechanical valve rotation addresses two of the major mechanisms for exhaust valve wear (adhesion and abrasive wear and build up of deposits and dent marks) which enables an increase in time between overhauls of exhaust valve assemblies. Figure 13: Photograph of valve spindle seat
FIELD TESTS AND SERIES OPERATION surfaces after 31,882 hours.
First MWH ReliaValve reached 37,505 hours operating experience Various engine field tests have been in progress Figure 9: Cylinder #1 of the MAN-B&W 7L70MC
since 2003, on several engine types and sizes. engine on the "MV Libra Buenos Aires / CMA
The results of the first four years were documented CGM Bahia" [6].
in [6]. One such field test was performed on the Figure 10 through Figure 17 show the inspection "MV Libra Buenos Aires / CMA CGM Bahia", which results and the reliability of the first ReliaValve on is powered with a MAN-B&W 7L70MC engine (see the "MV Libra Buenos Aires / CMA CGM Bahia". Figure 9). A new Nimonic exhaust valve and Thes pictures document the operation up to the Sentry Rotator were installed in 2003 in cylinder # 37,505 hour inspection performed in January 2010. 1 of this engine. As reported in 2007 [6], the The helix gear and the ratchet system were last Figure 11: Photographs of the valve spindle
ReliaValve had succesfully reached 16,647 hours inspected at 31,882 hours. Thes components and seat ring surfaces after 9,100 hours [6].
of operation. Periodic inspections at 1,000, 4,200, appeared in as-new condition with no visible wear. 9,100, and 16,647 hours of the general function of Figure 14: Photograph of valve spindle seat
the ReliaValve and, in particular, the seating surfaces after 37,505 hours.
MWH ReliaValve with Sentry Rotator MWH ReliaValve with Sentry Rotator DESIGN REFINEMENTS Effect of seating pressure on the removal of glassy-deposits from the valve spindle seat Hydraulic oil drains and air spring chamber The mechanism of the glassy-deposits was Field tests on an MC90 engine have lead to discussed in the beginning of this paper (see also refinements of the Sentry Rotator design. Figure 4, Table 1, and Figure 5). To remove these Specifically, improvements have been made to the hard deposits during engine operation, the hydraulic oil drains and air-spring chamber. This necessary and sufficient conditions are: refinement was done in 2006 and reported also in Seating pressure of more than 400 MPa Rotation of the valve spindle during closing The need for increasing the capacity of the hydraulic oil drains was necessitated by the large On most of the 2- and 4-stroke engines the seating oil flow requirement of large engine valve pressure of the exhaust valve spindles operate actuators. The addition of longitudinal grooves on below 100 MPa, see also [7]. The geometry of the the helical gear has increased the oil drain W-type bottom piece reaches seating pressures of capacity to handle flow rates in excess of 500 l/hr. 400 MPa or more. Similarly, after modifying the The air-spring chamber design has also been interference angle of the seat (changing the seat Figure 15: Photograph of the rotator gear and
modified. This was done in order to limit the angle of the valve spindle or changing the seat free-wheel after 31,882 hours.
maximum air pressure within the system and angle of the bottom piece), the necessary seating match the characteristic of the original air-spring, pressure with a minimum of 400MPa can be as shown in Figure 18 and Figure 19. achieved for exhaust valves with the common bottom piece geometries. To limit the valve spindle wear on the seat area, the seating pressure should not exceed 800 MPa. Figure 5 shows the seat area of a valve spindle Figure 20: Valve spindle seat with removed
(W-type geometry of bottom piece) with removed glassy-deposits (chamber type geometrie of
glassy-deposits at the contact area. In the majority bottom piece with modified seat angle for
of cases, MWH has seen that vane-driven valve higher seating pressure).
spindles do not rotate after the valve spindle seat initiates contact with the bottom piece during closing. With seating pressures above 400 MPa, the glassy-deposit layer is effectively destroyed in the seat contact area, but lacking rotation of the valve spindle seat against the bottom piece, the Figure 18: Comparison of the air-spring
particles of the glassy-deposits are pressed into the valve spindle seat, forming dentmarks and the Figure 16: Photograph of the outer helix gear
chamber pressure for original valve assembly
beginning of blow-byes. inside the valvedrive after 31,882 hours.
(no rotator), initial rotator (Evolution I), and
refined rotator design (Evolution II) [6].
To solve the newly observed problem with glassy- deposits, the MWH ReliaValve Evolution III was developed. This improved design combines the proven ReliaValve Evolution II with a new seat interference angle for higher seating pressure (more than 400 MPa). The end result is a very effective solution to combat the newly discovered and dangerous problem of glassy-deposits. These results can be seen in Figure 20, where the hard particles of the glassy-deposits do not create dentmarks during the closing process. Note that region "A" is the seat mating surface area that is both free of glassy-deposits and dents. Region "B" is the remainder of the seating area which, Figure 19: Comparison of the hydraulic drive
although covered by glassy-deposits, does not pressure for original valve assembly (no
negatively influence the operation of the valve (i.e. rotator), initial rotator (Evolution I), and refined
does not create blow-byes). rotator design (Evolution II) [6].
Figure 17: Photograph of the inner helix gear
after 31,882 hours.
MWH ReliaValve with Sentry Rotator An innovative and patented mechanical valve [1] Lampert, E., "Reducing Downtime for the 2- rotation mechanism has been developed for use in Stroke Engine," MER Magazine, November large 2-stroke diesel engines. This mechanical 2004, pp. 54-55, 2004. rotator (Sentry Rotator) can be incorporated into existing exhaust valve assemblies with minor [2] Fellman, H., T. Gross and T. Ludwig, "Typical additional modifications, and provides positive Wear Mechanism of 2-Stroke Exhaust rotation of the valve spindle during the closing Valves," Proceedings of the 2004 Marine process. Application of the Sentry Rotator Propulsion Conference. 2004. addresses the two main wear mechanisms in 2- [3] Kvernes, I, P. Kofstad and M. Seiersten, "High stroke exhaust valves (adhesion and abrasive temperature corrosion and protection of diesel wear, and build-up of deposits and dent marks), engine exhaust valves", Central Institue for thereby extending the service life of these Industrial R, University of Oslo, D101, CIMAC components. An engine field test program has resulted in some refinements to the rotator design, and ultimately to a well proven product. [4] Umland, F and M. Ritzkopf, "Valve corrosion in diesel engines" MTZ Vol36, No.7/8, pp. Based on the current operating conditions of 191-195 (July/August 1975). ecospeed or low-steaming, some cases of a new type of wear, the so called "glassy-deposits" on the [5] Kingston-Jons, M.G., J.R. Thomas and A. S. seat of valve spindles can also be eliminated by Radcliff, "Review of operating experience with increasing seating pressure and grinding effect current valve materials" Trans I MAR E (C), with the ReliaValve Evolution III. Vol. 102, Conference I ( 1990 ) pp15-28. Results obtained thus far demonstrate that a TBO of 30,000 hours, or more, are achieved for exhaust "Development of a Novel 2-Stroke Exhaust valve assemblies. Valve with a Mechanical Rotator to Achieve Three-Year TBO'S", Paper 84, CIMAC Congress 2007, Vienna. [7] Yamada, T, H. Sekiguchi and M. Mizushima, "Development of ceramic exhaust valves", Nippon Kokan, CIMAC D82 ,1985.

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