Photographic processing tanks

Description

[0001] Photographic processing tanks for processing lengths of exposed photographic film are well known and they consist essentially of a light-tight tank in which the film, arranged in a spiral coil, is supported on a holder. The film is loaded onto the holder under darkroom conditions, such as safelight illumination or in total darkness. The holder is then placed in the tank and the tank is made light-tight. Thereafter, the processing can be accomplished with the tank in normal lighting conditions.

[0002] The processing solutions are introduced in turn into the tank and they must move freely over the film surface so that solutions which have been exhausted in certain areas of the film emulsion may be moved to other areas of the film. Similarly, solutions which have not been involved in a great deal of activity, and are, therefore, not exhausted, must be moved to those areas of the film where interaction with the film emulsion is greater. This periodic movement of the processing solution is conveniently brought about by completely inverting the processing tank at regular intervals. To prevent processing solution from pouring out of the tank when it is inverted, it is usual to provide an outer seal cap which is arranged to cover the opening in the top of the tank through which the processing solutions enter and leave the tank and it is sealed around its periphery to the top of the tank.

[0003] During the processing of the film emulsion, gas is evolved and, as it cannot escape from the tank, the pressure in the tank increases.

[0004] It has been found in practice that, when the outer seal cap is eventually removed from the tank so that the processing solution can be poured from the tank, there is a tendency for the processing liquid to spurt. The solutions which are employed in film processing may be toxic and/or a skin irritant and it is undesirable that these solutions should spurt on to the operator's hands or clothes. It is even more important that the solutions should not be allowed to spurt into the operator's face as this may necessitate medical treatment.

[0005] It is known to make the outer seal cap of a flexible plastics material which moves outwardly under pressure (GB-A-2004849). However the reduction of pressure achieved by such a device may not be sufficient to avoid spurting when the tank is opened, because it is limited by the resilience of the material from which the cap is made.

[0006] According to the present invention, there is provided a photographic film developing tank including a manually operable valve means for lowering excess pressure in the tank, characterised by an inwardly facing valve seat formed on an inwardly extending threaded annular neck of the lid, a movable valve member mounted on the said neck by means of a threaded annular collar and resiliently biased into engagement with the valve seat, and a manually operable plunger mounted on the lid and extending through the valve seat to engage with the valve member.

[0007] In order that the invention may be more readily understood, it will now be described by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a sectional side elevation of a film processing tank; and

Figure 1a is an underneath plan view of part of the lid of the tank of Figure 1.

[0008] Referring to Figure 1, a film processing tank comprises a generally cylindrical open-topped container 1 containing a film holder 3. This holder has a central hollow tube 5 and at least one pair of annular support plates 7 removably mounted on the tube. The plates have spiral wound ribs thereon and the lateral edges of a strip of film to be processed (not shown) are located in the spaces between adjacent turns of the ribs. A lid structure 9 is removably mounted on the top end of the container 1 and, when it is so fitted, the lower end of a funnel portion 11 of the lid structure projects into the upper end of the hollow tube 5. The solutions required to bring about the various processing operations are poured in turn into the upper end of the lid structure and they flow down the hollow tube into the tank. Similarly, spent processing solution is removed by inverting the tank.

[0009] An outer seal cap 13 of resilient material has an annular, downwardly extending, rib 15 which fits tightly into an annular channel extending around the upper surface of the lid structure. A valve means 17 is located in the seal cap to enable pressure in the tank to be reduced before the cap is removed from the lid structure. In the arrangement shown in Figure 1, the cap has a central downwardly extending portion 19 with an aperture forming an annular valve seat 20 at its lower end. A valve assembly 21 has an annular threaded portion 22 which screws on to the portion 19 to cause a valve member 23 to engage with the valve seat on the underside of the aperture 20. The valve member is attached to the portion 22 by radially extending, resilient spider arms 23 (see Figure 1a) which form a biasing spring. A plunger 25 extends into the aperture 20 close to the valve member 23. Any build up of pressure in the tank urges the valve member 23 against the valve seat of the portion 19 to close off the aperture. To release the pressure, the plunger 25 is manually pressed downwardly from outside the tank to displace the valve member from the underside of the aperture.

Claims

1. A photographic film developing tank including a manually operable valve means for lowering excess pressure in the tank, characterised by an inwardly facing valve seat (20) formed on an inwardly extending threaded annular neck (19) of the lid (13), a movable valve member (23) mounted on the said neck by means of a threaded annular collar (22) and resiliently biased into engagement with the valve seat, and a manually operable plunger (25) mounted on the lid and extending through the valve seat to engage with the valve member.

2. A photographic film developing tank according to claim 1, in which the valve member (23) is connected to the said collar (22) by means of a plurality of radially extending resilient spider arms (24).

Ansprüche

1. Photographischer Filmentwicklungstank mit einem von Hand betätigbaren Ventil zur Verringerung des Überdrucks in dem Tank, gekennzeichnet durch einen nach innen gewandten Ventilsitz (20) auf einem sich nach innen erstreckenden, ringförmigen Gewindehals (19) des Deckels (13), einen mittels einer ringförmigen Gewindemanschette (22) auf dem genannten Hals angebrachten beweglichen Ventilkörper (23), der mit dem Ventilsitz federnd in Eingriff gehalten ist, und einen von Hand betätigbaren, auf dem Deckel angebrachten und zum Eingriff mit dem Ventilkörper durch den Ventilsitz ragenden Kolben (25).

2. Photographischer Filmentwicklungstank nach Anspruch 1, bei dem der Ventilkörper (23) durch mehrere, radial verlaufende, federnde Sternarme (24) mit der Manschette (22) verbunden ist.

Revendications

1. Cuve pour le développement de films photographiques comprenant une valve pouvant être actionnée manuellement pour abaisser sa pression interne caractérisée en ce que la valve comprend un siège (20) orienté vers l'intérieur de la cuve et formée dans le couvercle (13) un organe mobile (23) monté sur le col au moyen d'un collier annulaire fileté 22, et sollicité par une force élastique dans son engagement avec le siège de la valve, et un piston (25) manoeuvrable manuellement et monté sur le couvercle et s'étendant à travers le siège de la valve pour coopérer avec l'organe mobile.

2. Cuve pour le développement de films photographiques, selon la revendication 1, caractérisée en ce que l'organe mobile (23) est relié au collier annulaire (22) au moyen d'un certain nombre de bras radiaux élastiques (24).

Drawing