Dumpmaster - Servicing the hydraulic ram

Dumpmaster bin tippers use a single-acting displacement-type hydraulic ram, which is very reliable, but also easy to service should the need arise. There is no piston, just a seal in the head which seals onto the chrome-bar spear. A groove machined into the outside of the ram head locates into the ram-mounting bracket, which is welded to the mast. A ram-retainer (or hose clamp on older machines) holds the lower end of the ram into the bracket. The upper end of the ram locates into a special adjustable bracket.

The ram-end rollers should be running just clear of the mast throughout the full travel of the ram. If the rollers press hard against the mast at any point, they can cause the spear to “bind”, which may prevent the cradle from coming down properly.

The top bracket has four small tabs, which can be bent to ensure the ram is correctly aligned, particularly when it is extended. For example, if the rollers press hard against the mast when the ram is extended, bend the tabs so that the top of the ram is held nearer the mast.

Some machines are fitted with a Roller Guide Channel, to ensure the ram rollers track accurately. This needs to be removed before working on the ram or rollers. To remove the guide, firstly remove the bolt securing it to the ram-stop, then loosen the ram-retainer, and pull the guide downwards. Once the guide is removed, the ram rollers can be easily removed and replaced. To refit the Roller Guide Channel, simply place it in position, push upwards to engage the ram bracket, and replace the securing bolt.

Removal and refitting

1. Lift the bin cradle a little and sit it down on some timber or other suitable packing.
2. Remove the steel ram cover. Press the ‘DOWN’ button, while pushing up on the ram rollers, to fully retract the ram.
3. Undo the fitting holding the hydraulic tube to the power pack.
4. Undo the ram-retainer (or hose clamp on older machines) holding the ram to the mast.
5. Disengage the chains from the rollers, pull the bottom of the ram out from its support bracket, and then slide the ram down out of the top support bracket. If necessary, unscrew the hydraulic tubing from the ram port.
6. The tabs on the top bracket may need to be bent out a little to allow the weld at the top of the ram to come through. If so, they should be tapped back when the ram has been replaced. 
7. Refitting is a reversal of the above procedure.

Dismantling and servicing

1. Hold the ram body horizontally in a vice, with the roller end slightly higher.
2. Pull the chrome-bar spear right out of the ram body, and lay carefully aside.
3. Take the ram body out of the vice, and pour the small amount of remaining oil into a suitable container for disposal.
4. If the ram seal needs to be replaced, pick it out of its groove, using a small, sharp screwdriver. It is very difficult to remove without damaging it – it is usually best to just stab it and pull it out. Smear oil on the replacement seal and insert it into the groove, taking care that it is the right way up (with the cup section facing into the ram).
5. If there is a pinhole leak in a weld, it is generally best to fit a complete replacement ram body, and return the faulty one to Simpro for repair. If this is not feasible, mark the location of the hole, and grind a groove at least 3mm deep, and 10mm each side of the hole. If possible, weld using MIG or arc welder. If a welder is not available, it may be brazed, but difficulty may be experienced because of oil contamination. The seal will need to be replaced, if the hole is in the “head” weld.
6. Blow the ram out with compressed air, and clean the exterior with degreaser.
7. Wipe the chrome bar carefully, then fit it back into the ram body, using a twisting action as it goes through the seal.
8. Refit the ram as described in Removal and refitting above.