This tip was published in Maintenance Tips on Feb 22, 2007

Filter Tip
Check those filter head bypasses

Are the filters lasting longer than usual? Are particle counts up and changing filters does not help ?

If the filter head has a spring loaded bypass valve.... check it. Vibration can cause the spring, plunger or bypass plate to quickly wear through, putting the filter in continuous bypass or at least partial bypass with little or no indication in pressures. We had to replace 6 applications due to this. We finally went to filter heads with no bypass function.

Tip provided by Jerry Baker
PdM Team, Lubrication
Tate & Lyle
Loudon TN

It generated this response:

I enjoyed the article about filter head bypass. It is so true and is why companies must never just buy things of the shelf without the engineering and operations department team working as one. Too many time the guys in design just install a filter with protection for the pump, filter or flow and don't see the big picture.

It is many time better to use NO bypass and just install a differential sensor or good dependable gage to show when the filter is getting dirty. If the installation is critical and can't be shut down for a element change out, then you MUST install a duel filter with switchover valve or a bypass filter assembly.

Food for thought, don't go cheep on filters OR HEADS, or you may spend many times over to replace the equipment down stream of the filters. Don't forget the moisture separating elements either.

(Retired,) Staff Chief Engineer
Washington State Ferries

Mahalo

Clark Dodge, President
CED Consulting LLC
341 Lanakila Rd, Suite 100
Kapaa, HI. 96746-1241

Phone: (808) 245-7183
Cell: (808) 634-8183

Clark@CEDConsulting.com
http://www.cedconsulting.com

And this one:

I have a comment on your "Filter Tip" article.

While I can appreciate the problems outlined in the article the dangers of eliminating the bypass function of a filter is too great. The design engineer that felt the function was necessary in the first place would probably agree since he or she probably did a risk assessment and concluded that a clogged filter was greater harm than flowing unfiltered oil and the system had real potential for such a condition.

If the problem of wear out of the bypass components is the cause then perhaps a redesign is in order to address the issue. However, if this is considered normal wear, then perhaps a bypass indicator is in order. I did a short search and located a site where the manufacturer provides just such a device. http://www.purolator-facet.com/aswitch.htm. I am in no way associated with Purolator.

I'm sure other filter / accessory manufacturers have similar devices.

Scott B. Truax, CMRP
United Space Alliance. Processing & Manufacturing
Cape Canaveral Florida

The content of this e-mail is strictly the opinion of the author and is in no way endorsed by the management or ownership of United Space Alliance.

And this one:

The latest filter tip about partial bypass situations prompted this.

Three purchases were made for a certain Portable filter units, for a total of 8 units. The pumps were put in operation on hydraulic sumps and allowed to operate for 24 hours whenever needed. The system particle counts would drop as expected.

A bad pump required disassembly of 1 unit, where a 1/8 inch bored hole was noted between the pump discharge/filter inlet and the filter outlet section. This allowed a continuous bypass in the housing itself. Inspection of all 8 units revealed the same condition on all of them. Units were returned for plugging of the open port, with no explanation given as to the reason for the oversight.

Since repairs were made it is possible to get the same clean up in a couple of hours instead of 24.

I urge all users of this unit to inspect them closely.

Harold Matroni
Lubrication Technician/Analyst
Alcoa Mill Products

This message has been edited. Last edited by: Terrence O'Hanlon,

quote:

Harold Matroni

It would be helpful to know the brand and type of portable filter unit that had the hole in the head. I seem to get varying success in filtering oil with my portable filtering equipment, all purchased from one company. If it's the same company, I'll know to inspect the heads.
Regards,
Tom Brittain
Grant County Public Utility District

Why do we want to bypass the filter in the first place? What applications require filter bypass. 2 filters with a swapping valve is commonly used.

Tom

Harold reported this make and model:

HYDAC OF7 Portable filter

I hope that helps.

Josh

Most applications are kidney loop style, meaning that the pump for the filter loop is independent of the main function of the oil system. In that case, bypass doesn't make much sense (except possibly to protect the pump for the kidney loop).

But if you have a system where the filter is in-line with the main pump feeding the bearings or other important load, you definitely want a bypass feature to automatically (without operator intervention) allow the system to continue to function upon clogging of the filter. I assume the duplex fitlers you are talking about require manual shift, rigth?