Tanks & boxes

Tank locos; we have side, saddle, well and pannier tanks. What are the advantages and disadvantages of each type please, or was it just down to the designer's preference?
Since some preserved lines have two or more types in use, do crews notice any major difference in operating between say pannier and side or saddle tanks?

Similarly if the Belpaire firebox is an improvement on square fireboxes, why did both types continue in production?

 

Generally speaking, saddle tanks are more prone to injector issues as the water gets pretty warm in the tank. In their favour, however, they allow for easier access to the frames as opposed to side tanks.

Far from a definitive answer obviously, but it's one point...

 

The main issue with saddle tanks is stability as it give a higher centre of gravity than a side tank. However, where stability was not an issue then they found favour for ease of access to the inside motion over side tanks. Presumably pannier tanks were developed to try and get round the access issue but retain a lower centre of gravity.
I know from experience that trying to oil the inside motion of a side tank can be a dark and slightly claustrophobic affair where as a saddle tank gives much more light to see what you're doing. One problem with side tanks is the they are often fited with lifting type injectors which can be touchy when the water is warm and low in the tanks, saddle tanks are more usually fitted with flooding injectors which can make life easier unless, as Robert Heath No6 has suggested, the water is getting too warm.

 

Saddle tanks can get a bit awkward when the loco has a belpaire firebox. Another reason why pannier tanks are advantageous and why the GW used them on their 0-6-0T's. Well tanks have the advantage of keeping the centre of gravity low and making the chassis quite rigid. The valve gear and all the other bits have to be outside, though. They suffer from the fact that the injectors generally have to lift the water into the boiler and anybody who has had to do battle with lifting injectors will know the potential problems!
Few and far between are end tanks and belly tanks. An example of an end tank is No.2 Dolgoch on the Talyllyn. I don't think any belly tanks survive, certainly in the UK. These had the tank under the boiler but not between the frames; a bit like an inverted saddletank.
Nobody has answered your question about Belpaire fireboxes and square fireboxes. A bit confusing as don't think there is such a thing as a square firebox. A square firebox would be essentially a Belpaire firebox of square dimensions! Were you asking about Belpaire fireboxes and round top fireboxes? Both have their advantages and disadvantages. Round top fireboxes were generally cheaper to construct with less complicated flanging required and were generally lighter in weight. Belpaire fireboxes were considered to have a larger steam space, give a more constant surface water area and be easier to stay but were fairly complex in their construction.

 

You missed out well and wing tanks (which are effectively side tanks with a different name). The advantage of a well tank is that it makes use of an area that is often ignored and empty- between the frames- thereby lowering the CoG or increasing endurance (if normal side tanks are used as well). This is why a lot of narrow gauge engines use them particularly locomotives associated with the WW1 narrow gauge railways of both sides- long stretches of track and poorly laid track.

The advantage of pannier tanks is that they combine the lower CoG of side tanks with the ease of accesability to the motion that side tanks have, with minimal contact area between tanks and boiler. A lot of pannier tank engines were originally saddle tanks, especially early GWR designs.

 

One of the things I personally prefere about the pannier tanks, is that i find them more comfortable when taking water than a sadle tank or side tank, as there is a much bigger flat area to stand on.