The dulcetina style harmonium is very small and portable, but due to the small bellows and less than ideal spring force on the front reservoir bellows (which face the player), the sustain is not very good. Better for one or two note playing versus three or four note chords.
Here are two useful videos to help you work on a dulcetina:
The picture on the right shows a dulcetina from the top. There is a bellows on the back and one on the front. You pump the rear one and the front one is the reservoir for the reeds. This is equivalent to the internal bellows on a Delhi or Calcutta harmonium.
There are no stops or other 'bells and whistles' on a dulcetina.
In this next picture, the trim pieces above the keyboard have been removed.
This next picture shows the right side of the dulcetina with the side pieces removed and several parts identified. The keyboard sits on top of the main box where the front bellows are mounted with the reeds on the inside. It is hinged on the bottom and held closed by a metal latch on each side, as well as two Main Box screws on either side. This picture shows the Front Bellows Spring in the open position. The straight spring wire for the front belllows is shown resting against the box. There is a spring wire on either side of the front bellows which can be held in a latch (upper left of picture). Both springs should be latched to hold it closed during transport. However, these springs are quite strong and if both are engaged, the bellows will not move very much and the sustain will be very poor. With one spring disengaged the sustain is better, but with both springs disengaged, there is nothing but the folds of the bellows to squeeze air of the bellows.
Here is a right side view of the dulcetina with the side panel removed.
The Main Box holds the front bellows along with the reeds. There is a latch on each side used to hold the main box closed. This allows you to leave out the main box screws on either side while working on it.
With the Main Box screws removed and the latches opened, the keyboard and main box assembly can be hinged apart from the main bellows sub-assembly on the back. The key lifters which cover the reed holes are at 90 degrees to the keyboard and move towards the back of this picture when a key is pressed.
This picture is a rear view of the main box, with the rear cover laying flat. This exposes the key lifters and also shows the manifold for the main bellows and six small holes on the key lifter board, which channels the air into the reed chamber.
This picture is a view with the main box open, as seen from the opposite side of the reed and key lifter board relative to the picture above. The keyboard is vertical at the top of the picture for orientation. The open main box shows the reeds inside the box, and the front bellows (facing the player) on the other side. The three holes allow air to flow in and out of the front bellows, through the six holes in the above picture. which are covered by a trapezoidal piece of gray leather in the lower right corner under the reeds. This is a valve which controls the flow of air from the main bellows which are squeezed by the player, pressuring the reed box. The front bellows facing the player act as a reservoir. When the player finishes squeezing the main bellows and allows air to fill them, the valve closes so air is drawn from outside and not from the front bellows. In the more traditional harmonium, the bellows in the main case acts as the reservoir. The key lifters shown above are on the opposite side of the reeds...the rear of the main box.