Jav. Oil by- pass deletion.

[johnairey]

From ‘The Javelin’ Jan/Feb 2019 it is suggested that the by-pass valve be sealed off as the modern oil filter is man enough to take the full pressure of recommended maximum of 70lbs.
I have never seen this discussed on JT is this common practice? Is it safe?

[trymes]

John,

I can't add anything to this conversation, but I am interested to hear what others have to say.

Also, it looks like you inadvertently created three copies of this thread, so you may want to delete the other two to avoid having replies in three different places.

Tom

[Nick Webster]

I am not sure why you would want or need to do this. The pump is certainly capable of much more than 70 psi, as I found out when test driving a car that had not been run for a while and looked down to see the gauge approaching 100psi. At first I thought it must be the gauge but realised the reading was speed related and perhaps the pressure relief was stuck. After changing both oil and dirty looking filter everything has been ok so I haven't had to worry about going into the pump. Yet!

Nick

[PJGD]

I assume that you are talking about the filter bypass valve in the filter housing. Back in the day under cold start conditions with single grade engine oils it was, I suppose, quite possible under extreme conditions for the pressure to build up ahead of the oil filter and rupture the filter element. In that situation you might not know that the element had failed and you would carry on driving with unfiltered oil reaching the bearings for months until the next oil and filter change. With the bypass valve installed, the ball valve would pop open against its spring and a relatively small quantity of unfiltered oil would get through. Clearly this is the better of the two scenarios.

I have not seen anything to suggest that modern filter elements are more robust against over pressure than the original Vokes or Tecalamite elements were, but I think that the likelihood of a filter bursting or the bypass popping open with modern oils, particularly multi-grade oils, would be very unlikely. I do not see a problem that would make me want to go the the trouble of de-activating that bypass valve. Anyway, the issue is only likely to occur under very cold ambient conditions when most people are not driving their Jowetts - assuming that it even starts in those temperatures!

[johnairey]

The question I had on my mind was what pressure the by-pass valve is set at. The oil pressure was increased to 65-70lbs at the 1951 change with no mention of an adjustment to the filter by-pass valve.
The by-pass valve is a sealed unit. The two spare ones I have I connected to an air line and both registered a blowoff pressure of 50lbs which is below the 70lbs the oil pump is set at. Is there an allowance made for the thinning of the oil at running temperature for a designed 50 lb running pressure?

[PJGD]

Your air pressure test only applies pressure to one side of the valve, but the valve works on the differential pressure across it. We don't know what pressure is on the up-stream side, whereas the pressure on the downstream side will be what you are reading at the pressure gauge plus a little bit for losses in the gallery drillings. In other words, that is the pressure assisting the spring trying to hold it on its seat on the back side. We don't know the differential force acting on it which is the pressure drop across the filter element.