Have you ever dealt with Parker’s Gold Cup pumps? If yes, you probably noted in the product datasheet, this pump does not require to have filtration of internal charge (boost/replenishing) pumps flow. There is just a short recommendation “the auxiliary pump fluid be filtered to aid in maintaining acceptable cleanliness levels”:
The reason for that is because Parker thinks all close loop systems need to be designed to ensure “the oil tank is protected through filtration from any ingress contamination”. Later I shall show you Parker’s document where this statement is coming from (AS-0018). Actually, question to you: do you agree with this statement?
I do not. I use charge (boost/replenishing) flow filtration for every single close loop pump at every single project via an external filter connection. Moreover, both proportional and servo control systems require even more fine cleanliness level of the element for filtration, therefore for such systems I use two separate filters: for charge flow (usually 10 mkm element) and for servo control flow (usually 2 mkm element).
But there are a couple of problems with the Gold Cup pump external filtration. Although these pumps have ports for external filtration and even a short guide in the datasheet on how to make filtration (screenshot above) due to design of internal galleries is different for all three Gold Cup pump frame sizes, and, in addition, is different for specific side a control system is mounted on, you will not be able to provide a correct filtration and even can destroy the pump if connect external filter in the wrong way. And this problem is not explained and not resolved in the product catalogue.