Flow regulator for vacuum pump

[jiyoo]

I am looking for a regulator for vacuum sampling system.

I'm collecting the particles on the filter and the pressure drop keep increase then I have to adjust (open) the valve for vacuum pump. Is there a sort of regulator to keep the flow through the filter? I guess the vacuum regulator or flow regulator would be fit, however, I don't know the specific product.

Thanks in advance.

Jay