More than one com.day.cq.replication.Preprocessor

We have a site in AEM 6.1 SP1 where we had to include a second preprocessor - there was already one performing some tasks on page activations and now we need to perform additional tasks during the same process. By simply creating another @Service that implements com.day.cq.replication.Preprocessor, the system is only executing the first one, and not the new one. 

Is there any restriction on the number of PreProcessor that can exist? Is there any additional configuration needed to guarantee that all the services will be executed. I did not find enough documentation or samples on having more than one.

Thank you.