The volume goes up anytime,does not matter if it s an large order or an smaller trade,because it s starting from 0 and on the end of the day can be any number depending of how many person buyed and selled.
On meta trader you will notice that you have an volume indicator that you can put and also you will notice that if somebody buy or sell same time the volume will increase with 2 points,and so on.
If they where 5000 orders of buys and 10.000 orders of sells the total volume will be 15.000,but that can differ because some are doing large or small trade,anyhow the idea is that the volume goes up from the start of the day.
It`s starting from 0 to how much it`s traded and reached on that day or how many contracts are done.
Volume as seen from the terminal is nothing more than a tick counter. All it tells you is that there has been a trade.
I think the actual question 1ken89 should be asking is what happend to liquidity?
There can be no doubt that liquidity is taken out of the market when a trade is executed. There are 2 ways to look at this. If the trade is placed in the system as a pending order, it contributes to the liquidity pool. When the trade get executed by price movement, liquidity will be absorbed by this trade. If the order is a limit order(price MUST be better than requested) and there is insufficient depth of liquidity, the order may be split and only part filled........if the order is a stop order, the full order will be filled at whatever liquidity is available. I am not sure if the broker will give the whole trade the price at the last fill, or whether they will cost average the price as the actual price is slipped along the available liquidity.
If at any time the trade is executed as a market order, it only ever absorbs liquidity. Many brokers have alternative routings for big orders that may adversly affect their liquidity pools.
It would be interesting to hear from the guys that have some inside information whether stop orders contribute to the liquidity pool in the same way as limit orders do.