Basic Pump Question

When you say "can only build up so much pressure in the downstream pipeline" you mean centrifugal pumps are designs like this that they have some type of relief mechanism? So this is the correct type of pump for this application? (sorry I know it's basic but I want to be sure I understan).

Most fuel delivery pumps use a bypass or relief system so pump can be dead headed. You need to contact a pump manufacture for information on same.

http://www.irrigationcraft.com/pump_curves.htm

In the example shown in the link above, the maximum delivery head is 250ft and the flowrate is zero at that head. All the designer has to do is make sure everything downstream of it can withstand that pressure, and no other equipment is required.

These are most likely to be centrifugl pumps and they are meant to handle these conditions. The problem that you envisage would be with PD (positive displacement) pumps which are more likely not useful here except some special ones (like diaphragms ) due to metallic contact and rubbing.

I do know a thing or two about fuel delivery systems, and you got it pretty much dead on. Most fuel systems are designed with a high pressure cut off for the pump and / or a pressure relief that recirculates the fuel back to the tank.

If it is not fully enclosed with housing you don't have access to, look at your system. There should be a small wire going to the discharge side of the pump; it could be located right at the pump or anywhere downstream. The wire should go to a controller that reads the pressure or flow and will switch the pump off when not needed.

A recirculation system should be a pressure relief valve located just downstream of the pump with a return line going back to the tank. Uncommonly, the pressure relief line will recirculate directly back into the inlet of the pump and could be internal to the pump casing.

You would know if it was an always on system because it would kill the battery quick. You can switch the pump on and feel the casing, if it warms up quickly during low flow conditions you probably don't have a recirculation.

Drew K

That's alright, everyone has the right to comment,we don't take any notice of you anyway!

Bazzer

Actually for any kind of fuel delivery it is better to go for gear oil pump. So when you check for any kind of information please check for GEAR OIL pump.

The viscosity of gasoline is far too low to use a gear oil pump. You are likely to get zero flow.

Most fuel transfer pumps involving handheld dispensing nozzles are vane pumps (occasionally diaphragm pumps). These ones are typical.

what I do recall with a very brief career as a service station technician was that there was a pump call contactor with each noozle lifted.

Further, a built in recirculation-relief system within the pump head itself.

Believe pump was Veeder Root--not sure. Can google Demarco (fuel oil station mfg) and possible get more details.

Yes that is true, basically the dispensers motor (pump) is off and when the nozzle is lifted the pump "calls" (i.e. requests) authorization from a controller. Only then is the pump motor activated. (but still, the pump is running and the nozzle valve is closed so question remains)

There is a lag time upon pump hang up.

Again, going on recall from a long time ago but remember 15 sec's.

I do recall clearly (at that time -13 YAG) that with inactivity, pump (singular) turned OFF.

Pump ramped up (don't remember but not VFD) with multiple noozle lifts and vice versa.

then lag time with last hang up.

Google Veeder Root and Demarco-debarco (not sure). You'll get better details unless a response from a dedicated service technician for fuel oil stations.

the pump is running and the nozzle valve is closed so question remains

With due respect to all, Znago stated 'no knowledge' up front...

So Znago, keeping engineering terms to a minimum, your pump operates much like your office desk fan/ or your aircon unit. It blows air forwards because the blades are angled that way, and so it rotates in one direction only, in order to blow the air. You must have seen those inflatable 'jumping castles' that one can hire for kiddie's parties and such.(named so in my part of the world anyway...they come in all shapes and sizes), These are kept constantly inflated by an air fan, blowing (pumping) air through a tube of the same diameter as the fan. Any number of persons can climb aboard and jump, yet the thing doesn't deflate while the fan is running. The weight of the 'jumpers' on board cause a lot of back-pressure to the fan. This back-pressure of the air in the inflatable becomes greater than the 'blown', or supply pressure from the fan and simply flows back around the fan blades, with no damage to the fan.

The jumping castle also never bursts from over-pressure.

This is the principle of your centrifugal fuel pump, which is designed to pump a liquid. It too has blades (many of them), and works the same way as the air fan. The 'head' referred to by others here, is the pressure against which it operates ie your closed dispensing hose causes a maximum pressure head. The 'fan' inside the pump is the impeller, and this has sufficient clearances to allow the liquid back-pressure caused by the closed hose-nozzle, to pass back through and around the impeller, so that the discharge pressure reaches a maximum value which cannot be exceeded due to the impeller design. This maximum is designed to be safe for your hose and nozzle assembly.

NB each type of application has a different design pump....I am only explaining the system you described in your query.

'nuff said..you've been spoilt !