Tried to link to the Sale Blanket Orders app/module here, but somehow the Forum wouldn't let me (403 Forbidden error) - search in the app store, it looks pretty good and recently maintained, but not a solution for Online edition.

This requirement is standard OpenERP functionallity.

1. Create an order with quantity of 50 PCE
2. Confirm the order
3. A new outgoing shipment is created

If the state of the shipment is Available then the products are reserved. Otherwise you can force the reservation with Force Availability.

Then when you want to ship 10 PCE of the order, you just have to create a partial picking by clicking Deliver and choose how much you want to deliver.

Then a new picking is created with the chosen quantity (10 PCE) and is processed immediately.

The quantity of the original picking is set to 40 PCE and remains in state Available.

You can perform such partial pickings as often as you want.

Update for recurring shippings:

As noted in question https://accounts.openerp.com/forum/Help-1/question/1560/ you can define recurring objects.

So you can also define recurring outgoing shipments. But then the already shipped quantity will not be subtracted from the original shipping. If you exactly want to implement you intended functionality you have to write a short module I guess.

Thx for your help! i appreciate it!