Valves and valve actuation – Fluid actuated or retarded – Dashpot or fluid controlled retarder or timer
Reexamination Certificate
1999-03-10
2001-02-20
Shaver, Kevin (Department: 3754)
Valves and valve actuation
Fluid actuated or retarded
Dashpot or fluid controlled retarder or timer
C251S048000
Reexamination Certificate
active
06189856
ABSTRACT:
TITLE: PRESSURE RELEASE VALVE
This invention relates generally to fluid pressure release valves. The invention has been devised primarily in the context of steam peeling equipment used for removing skins from potatoes or other hard produce. However, it is to be understood that the invention is not limited to this particular application.
Steam peelers are well-known in the art of potato processing. Essentially, a steam peeler comprises a large pressure vessel into which successive batches of potatoes are introduced. A batch may comprise approximately 500 Kg of potatoes. After a batch of potatoes has been loaded, the vessel is sealed and saturated steam is introduced under pressure to a level of approximately 13 or 14 bar. The vessel is rotated to ensure steam contact with the potatoes. This steaming phase lasts a relatively short period of time, for example, about 35 seconds. The pressure is then abruptly released, which causes the potato skin to be explosively separated from the remainder of the vegetable.
Precise control of the operating parameters of the peeler is necessary in order to ensure that, on the one hand, the skins are completely removed from the potatoes while, on the other hand, undue amounts of the vegetable itself are not removed with the skins. Abrupt release of the pressure is particularly important. Conventionally, the pressure vessel is fitted with a rotary pressure release valve for this purpose. Commercial valves generally have been found to have a minimum valve exhaust time in the range of five to seven seconds (the time for 14 bar pressure within the vessel to decay to 0.5 bar). While this is adequate, it is believed that improved performance can be achieved with shorter valve exhaust times.
Valve life has also been found to be relatively short with conventional valves. For example, a typical maximum life may be about 600 hours of operation. Not only are the valves expensive to replace, but significant “down time” is required to replace a valve.
Examples of prior art steam peelers are shown in U.S. Pat. Nos. 4,064,794 and 4,091,722, (both to Kunz) and also in U.S. Pat. No. 4,188,869 (Komen). These patents relate primarily to closure devices for the opening in the pressure vessel through which the potatoes are loaded into and removed from the vessel, rather than to pressure release valves as such.
Other U.S. patents of background interest are as follows:
U.S. Pat. No. 2,728,547 (Cookston et al.)
U.S. Pat. No. 2,778,598 (Bolling)
U.S. Pat. No. 3,024,801 (Carls)
U.S. Pat. No. 3,243,156 (Shoemaker)
U.S. Pat. No. 4,484,545 (Madsen)
U.S. Pat. No. 5,292,103 (West et al.)
In general, these patents failed to address the need for a pressure release valve that is suitable for use on the pressure vessel of a steam peeler and that provides for a very short valve exhaust time.
Accordingly, an object of the present invention is to address these shortcomings of the prior art by providing an improved pressure release valve that is suitable not only for a steam peeler pressure vessel but also for other pressure release applications.
The pressure release valve provided by the invention has a valve body with a port for communicating with a pressurized fluid. The valve body also includes a cylinder receiving a piston which is movable between the first position for sealing the valve port and a second position clear of the port. The piston is movable to the second position by the pressure of the fluid. The valve body includes vent means communicating with the port when the piston is in its second position, for venting of the fluid from the valve. The piston forms part of a differential piston assembly which also includes a fixed piston element in the cylinder. The piston element and the piston together define a chamber for containing a cushioning fluid, which has a maximum volume when the piston is in its first position and a minimum volume when the piston is in its second position. Means is provided for controlling flow of fluid out of the chamber for cushioning movement of the piston. The valve also includes piston actuating means for maintaining the piston in its first position when the port is to be sealed, the actuating means being releasable to allow the piston to move to its second position under the influence of the pressurized fluid when the pressure of the fluid is to be released.
In other words, the invention essentially provides a differential piston pressure release valve in which the piston can abruptly be driven by the pressurized fluid from the “valve closed” position to the open position when the piston actuating means is released. At the same time, movement of the piston is cushioning by the cushioning fluid so as to minimize the risk to damage of the valve that would occur if unrestrained movement were possible.
In a steam peeler, the piston may be steam actuated using an external steam supply, i.e. not the steam from the pressure vessel. In this case, the piston will be held in its first (closed) position by the pressure of the externally supplied steam. When the steam supply is terminated, the pressure of the steam within the vessel will drive the piston to its second (open) position. A valve of the form provided by the invention may be used to control the supply of steam for actuating the piston, as well as for releasing pressure from the pressure vessel.
It should be noted that, in other applications, the piston actuating means may be designed to release the piston at a pre-determined threshold pressure, in which case, the valve would in fact operate as a pressure relief valve.
REFERENCES:
patent: 833473 (1906-10-01), Mesta
patent: 839862 (1907-01-01), Locke
patent: 1525859 (1925-02-01), Ferrari
patent: 1827725 (1931-10-01), Baker
patent: 2728547 (1955-12-01), Cookston et al.
patent: 2778598 (1957-01-01), Bolling, Jr.
patent: 3024801 (1962-03-01), Carls
patent: 3064675 (1962-11-01), Johnson et al.
patent: 3147827 (1964-09-01), Weisheit
patent: 3243156 (1966-03-01), Shoemaker
patent: 3531078 (1970-09-01), Hose et al.
patent: 4303378 (1981-12-01), Hunter
patent: 4484545 (1984-11-01), Madsen
patent: 4566273 (1986-01-01), Baumeler
patent: 5253671 (1993-10-01), Kolenc
patent: 5292103 (1994-03-01), West et al.
Bastianelli John
Bereskin & Parr
McCain Foods Limited
Shaver Kevin
LandOfFree
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